Of the 3,141 counties and county equivalents in the U.S., none has voted for the winner of every presidential election. Vigo County in Indiana has come close, backing 30 presidents starting in 1888, but its record was marred by its pluralities for William Jennings Bryan in 1908 and Adlai Stevenson in 1956.

But some counties matter more than others — especially those in states whose electoral votes are up for grabs. This year's presidential nomination contests did not proceed according to form, with far more votes cast for Donald Trump and Bernie Sanders than almost any expert predicted. It's not clear whether the patterns of partisan support that have mostly prevailed over the last two decades will be altered much in the general election; initial polling suggests, possibly misleadingly, that they will.

To gauge that, the Washington Examiner has selected 13 key counties to watch in eight target states with 114 electoral votes that have been seriously contested in recent elections. Each county has the potential to indicate who will carry these states.

1. Wake County, N.C.



Wake is the largest county in the nation's ninth largest state. North Carolina is sharply divided between fast-growing metro areas with major universities and high-tech and finance industries and a tradition-minded rural and small town hinterland. The state capital of Raleigh and surrounding Wake County sit in the middle — on the Piedmont between the coastal plain and the mountains, and next door to university-dominated Durham and Orange counties (70-plus percent Obama) and country music and barbecue haven Johnston County (63 percent Romney).

Wake County's dynamic economy has attracted newcomers from the Tar Heel countryside and from Northeastern cities (the satellite town of Cary is known as "Concentrated Area of Relocated Yankees"). With a population that is 20 percent black, 8 percent Hispanic and 5 percent Asian, Wake County has been voting about 6 percent more Democratic than North Carolina as a whole and moving in line with statewide political trends.

Wake County favored Barack Obama in 2008, when he carried North Carolina by 1 point, and gave him a reduced percentage in 2012, when Mitt Romney carried the state by 2 points. Wake County's large upscale population has leaned Republican but may be resistant to Trump, who lost Wake County in the March 15 primary to Ted Cruz 40-29 percent.

Hillary Clinton's challenge will be turning out black voters, who voted heavily and in large numbers for Obama in 2008 and 2012. In the 2008 primary he carried Wake County over Clinton 64-35 percent. This year her 69,000 votes there were enough to beat Sanders and were more than the 57,000 she won in 2008, but were far short of the 105,000 Obama won eight years ago. North Carolina has 99 other counties, but Wake County is the one to watch.

2. Hillsborough County, Fla.



Florida is the nation's third largest state, and its 29 electoral votes are famously closely contested.

It is also a state where most residents come from somewhere else: only 21 percent of adults over 25 were born there, a lower percentage than in any other state but Nevada. Five 2016 Republican presidential candidates have houses in Florida, but only one, Marco Rubio, grew up there. Floridians come from many different places — New York and Cuba, the industrial Midwest and the Deep South — and bring their politics with them. Broward County with its many ex-New Yorkers votes two-thirds Democratic, and the "redneck Riviera" panhandle counties with their many white Southerners votes two-thirds Republican.

In between, geographically and politically, is Hillsborough County, including the city of Tampa and its northern and eastern suburbs, with grandiose mansions on Tampa Bay and verdant orange groves farther inland. It's part of the Interstate 4 corridor that runs across central Florida through Disney World and Orlando to Daytona Beach. The highway's western terminus is in downtown Tampa, a few blocks from the site of the 2012 Republican National Convention. About one-third of the county's adults are Florida natives, while the others come from many places, leaving Hillsborough County about as ethnically diverse as Florida as a whole: 57 percent white, 15 percent black, 22 percent Hispanic, and 3 percent Asian.

In every presidential election since 1880, with the single exception of 1960, Hillsborough County has voted for the candidate who carried Florida. Over that time, Hillsborough's electorate has increased from fewer than 3,000 people to more than half a million. Few people noticed that Hillsborough County voted for Winfield S. Hancock in 1880, but many stayed glued to their TV sets to learn that it voted for Obama in 2012. Trump and Clinton both carried the county March 15, but only one will win it Nov. 8.

3. Stark County, Ohio



No Republican has been elected president without carrying Ohio, and since 1900 only two Democratic presidents, Harry Truman and John Kennedy, were elected without carrying the Buckeye State.

Ohio once had 26 electoral votes, in the 1930s and 1960s, but its heavy industrial economy has generated few new jobs over the last 40 years and it has had minimal population growth. But it still has 18 electoral votes and remains closely balanced between the two parties, voting by narrow margins for every winning presidential candidate over the last quarter century.

Cleveland's Cuyahoga County is heavily Democratic, Cincinnati's Hamilton County historically Republican, Columbus's Franklin County trending Democratic. But none comes as close to the statewide average as Stark County. Its largest city is Canton, home of President William McKinley, whose appeal to working men led to a generation-long era of Republican political dominance from 1896 to 1930, as Republican strategist Karl Rove has vividly chronicled in his 2015 book The Triumph of William McKinley.

Stark County has suffered job losses in recent decades, but remains both predominantly blue collar and, compared to Cuyahoga County or the former steel center of Mahoning County, Republican-leaning. It has not always voted for the same candidate as the state — it went for John Kerry over George W. Bush in 2004 — but its Democratic percentages have been within 2 percent (and its Republican percentages within 3 percent) of the statewide averages in the last eight presidential elections. In the 1896 election, McKinley hosted hundreds of thousands of supporters sent in by train in his "front porch" campaign, and McKinley's Stark County front porch, carefully preserved, remains a good vantage point for elections today.

4. Loudoun County, Va.



From 1952 through 2004, Virginia was a safe Republican state in presidential elections, straying from the fold only — and narrowly — in 1964. But the spread of metro Washington over the Northern Virginia countryside, the influx of Hispanic and Asian immigrants, and the growth of gentrifying young college graduates in its big metro areas have made Virginia with its 13 electoral votes a key marginal state. It's the state that came closest to matching the national percentage for the major party presidential candidates in 2008 and 2012.

These changes have been most visible in Loudoun County, west of Washington's Dulles International Airport. Formerly known for its Civil War battlefields — it was the northernmost point of the Confederacy — Loudoun County was still a sleepy backwater when Gen. George Marshall bought a house in Leesburg in the 1940s. But high-tech and government contracting companies moved out past Dulles half a century later and in the 2000-10 decade, Loudoun County was one of the nation's fastest-growing counties. It is also far more racially diverse than post-World War II suburbs, with a population that is 7 percent black, 10 percent Hispanic and 12 percent Asian.

Politically, Loudoun County has been a trend-setter for Virginia. Its racial diversity and the government orientation of many of its businesses have made it more Democratic than rapidly growing exurban counties in other parts of the country, but its high rates of family formation and exuberant economy have made it more Republican than closer-in Washington suburbs with their many singles and many more immigrants.

In the past four elections, Loudoun County has voted increasingly close to the statewide average in presidential elections, giving Bush 56 percent in two elections and Obama 54 and 52 percent, even as turnout increased from 75,000 in 2000 to 160,000 in 2012.

The county, with its upscale and young electorate, will be challenging for Trump, who lost the county to Rubio 40 to 28 percent in the March 1 Virginia primary. But it may be a challenge as well for Clinton, although she carried it over Sanders, because Democratic turnout was far lower than Republican, 36,000 versus 51,000.

5 and 6. Boulder and Douglas counties, Colo.



If you list the states in order of percentage for Obama in 2008 and 2012, you will find that he won his 270th electoral vote, the election-winning majority, in both years in Colorado.

It's a fast-growing state with a young, upscale population and the nation's lowest obesity rate, where most people live on a thin strip of land where the Great Plains meet the towering Front Range of the Rockies. Colorado's electorate is divided not so much along economic or ethnic lines as it is by cultural attitudes — differences made vivid in the contrast between two counties at the northern and southern edges of metropolitan Denver, which have similar-sized populations and similar ethnic balance but very different political views: Boulder and Douglas counties.

"The future is here and it works," writes Britain's left-wing Guardian newspaper about Boulder, home of the University of Colorado and the national center of extreme sports enthusiasts. It's prosperous, trendy, appreciative of nature, though perhaps too much so: several years ago a local jogger was eaten by a bear.

Boulder County is not especially diverse — 80 percent white, 1 percent black, 13 percent Hispanic, 4 percent Asian — but it is solidly liberal, voting 72 and 70 percent for Obama in 2008 and 2012, respectively.

Douglas County, south of Denver, is similar ethnically — 86 percent white, 1 percent black, 7 percent Hispanic, 4 percent Asian — but very different politically. It voted 65 and 67 percent for Bush and 62 percent for Romney in 2012. Douglas County is upscale but not the abode of the very rich. It has many young families, young parents who battled for school choice against the local teachers union and active churches with young congregations.

Each county has similar weight on the political scale: Boulder County cast 179,000 votes in 2012, Douglas County 168,000. Boulder County did not vote overwhelmingly Democratic until 2004; Douglas County has long been heavily Republican, but used to be much more lightly populated and, with its high growth rate, is likely to form a larger part of the American future than Boulder County.

A key question in Colorado politics is which county will outweigh the other. When Douglas County casts a higher Republican percentage than Boulder County's Democratic percentage, Colorado goes Republican, as in 1996, 2000 and, by a narrow margin, 2004. When it's the other way around, Colorado goes Democratic, as in 2012, 2008 and, by a narrow margin, 1992.

7, 8 and 9. Bucks, Luzerne and Mercer counties, Pa.



Some political analysts still rate Pennsylvania as "safe blue," because it has voted Democratic in the last six presidential elections. But not usually by wide margins, and in 2012 metro Pittsburgh, hugely Democratic in the 1980s, voted for Romney. Western Pennsylvania, heavily blue collar and elderly in population, has been trending conservative in recent decades, and central Pennsylvania remains heavily Republican. But eastern Pennsylvania, dominated by metropolitan Philadelphia, has been trending Democratic, with increasing percentages of blacks and Hispanics in suburban counties and city wards and because of the cultural liberalism of upscale suburban whites. Hence, we look at three counties to understand Pennsylvania.

Bucks County, northeast of Philadelphia, is 89 percent white and divided into two distinct areas. Lower Bucks is a collection of industrial towns along the Delaware River northeast of the city; it has voted solidly Democratic and casts about 35 percent of the county's votes. Upper Bucks, hilly and bucolic, once famed as the summer home of New York show business folk, is more affluent and was once heavily, and has been now more moderately, Republican. The county voted only 50 to 49 percent for Obama in 2012; Democrats hope upscale voters' unease with Trump will enable Clinton to do better this year.

Luzerne County, in northeast Pennsylvania, was once the center of the anthracite coal industry, but the mines have mostly been shut and the tight-packed century-old towns along the Susquehanna River are low-income territory now, with many white ethnics but only 8 percent non-whites. Those areas still vote Democratic, but there was genuine enthusiasm there for Trump, who won 77 percent of the vote in the April 26 Republican primary, his best percentage in Pennsylvania and one of his best in the nation. The county, and other communities like it in central Pennsylvania, look favorable for Trump.

Mercer County is at the western edge of Pennsylvania. The focus here is on Sharon, in the first half of the 20th century a booming steel and electronic machinery town, more recently an ailing city such as nearby Youngstown, Ohio. Rural parts of the county were among the most Republican parts of the country for three-quarters of a century after the Civil War, but Sharon and Mercer County moved decisively toward Democrats with the unionization of the steel industry in the 1930s. But in the last three elections, like most of traditional coal-and-steel country, they have moved toward Republicans.

All three of these Pennsylvania counties are about 90 percent white but are split between blue-collar and white-collar communities, and have seen political shifts among both groups in the last two decades. Will blue-collar Pennsylvania shift to Trump enough to overcome any white-collar shift to Clinton?

10. Hillsborough County, N.H.



The prime local units in New England have been towns from the time they were settled in the colonial era until today; county boundaries tend to enclose random collections of towns in New Hampshire as they do in the other five New England states. That said, Hillsborough County, named after the British colonial minister who stoutly opposed the colonists' demands, is as representative as any county in New Hampshire.

It includes the state's two largest cities, Manchester and Nashua, for many years the site of America's largest textile mills, now centers of high-tech businesses. It includes affluent towns near them and on the Massachusetts border; these tend to be among New Hampshire's most Republican communities, while Manchester and Nashua deliver small Democratic majorities. Further to the west are Peterborough and smaller towns known for decades as summer home communities and artist colonies; one of them, Hillsborough, was the birthplace of President Franklin Pierce in 1804. Like Vermont, western Massachusetts and western New Hampshire, these historically Republican communities have trended Democratic as old Yankee farmers have died out and are replaced by newcomers interested in environmental and anti-war causes.

Hillsborough County voted 50 to 49 percent for Obama over Romney in 2012, 2 points less Democratic and more Republican than the state as a whole. In the 2012 presidential primaries it split among the Republican candidates, as the state did, and its Democrats voted 57 percent for their Vermont neighbor Sanders in the primary. The increasingly upscale nature of New Hampshire's economy and population makes this target state a tough challenge for Trump.

11. Cedar County, Iowa



Only 37 of the nation's 3,141 counties contain the birthplaces of American presidents. Among them is Cedar County, the boyhood home of President Herbert Hoover. Cedar County is part of Iowa's rolling prairie running not far west of the Mississippi River, some of the richest farmland in the world. To the east is Davenport, the largest of the four Quad Cities on both the Iowa and Illinois banks of the river. To the west are Cedar Rapids, Iowa's second largest city, and Iowa City, home of the University of Iowa.

Cedar County owes its place on this list to the fact that it has come uncannily close to mirroring the Democratic and Republican percentages of the target state of Iowa in the last seven presidential elections, never varying more than 1.3 percent from average. Thus it voted 52 to 47 percent for Obama in 2012 and 54 to 44 percent for him in 2008; it voted 50 to 49 percent for Bush in 2004; and in the exquisitely close election of 2000, it went for Al Gore over Bush by a plurality of exactly two votes.

Why Cedar County has been so typical of Iowa is not clear. Before 1988 it voted consistently more Republican than the state, but moved toward Democrats, in line with a regional trend in eastern Iowa and western Wisconsin. That has made this beautiful countryside one of America's few Democratic-voting rural areas west of Vermont.

12 and 13. Clark County, Nev., and Maricopa County, Ariz.



Two other key counties are in states that didn't quite achieve target status in 2012 but each of which may be targeted by the party losing them in 2016.

Each of them tends to determine election outcomes in its state, for the simple reason that each contains a large majority of the state's voters. Clark County, which includes Las Vegas and its suburbs, casts 68 percent of the votes in a state with six electoral votes, and is a bit more Democratic than the rest of the state. Maricopa County, which includes Phoenix and most of its suburbs, casts 60 percent of the votes in a state with 11 electoral votes. These were the nation's fastest-growing states and counties in the years leading to the 2008 financial crisis, and after some harsh reverses are growing again. Maricopa County cast nearly 1.4 million votes in 2012, more than any other county except Los Angeles and Cook, Ill. Clark County cast almost 700,000, the 14th most of any county. Don't look for Nevada to go Republican or Arizona Democratic this year unless there are big changes in these two counties.