Think of a place that exports a lot and you might picture a bustling seaport, such as New York or the Los Angeles/Long Beach complex. But the most export-dependent places in the United States often are far from the big cities, and are much more likely to be in the South or the Midwest than on either coast, according to a Pew Research Center analysis of county-level data compiled by the Brookings Institution for its “Export Monitor” project.

Local economies that rely heavily on exports, in turn, have a lot at stake as multiple trade disputes play out between the U.S. and China, Mexico and other trading partners.

Measured as a share of gross domestic product, four sparsely populated parishes (Louisiana’s county equivalents) outside New Orleans are the most export-reliant localities in the country, according to the Center’s analysis. Those parishes are home to several giant oil and gas refineries and petrochemical plants, which account for the great majority of their exports. Taken together, exports from those parishes totaled more than $11 billion in 2017, or nearly two-thirds of their combined GDP.

The story is similar in Hancock County, Kentucky, outside Owensboro. The county, whose economy is dominated by aluminum smelters and aluminum products companies, exported $417 million in goods and services in 2017, or about 57% of its total GDP.

Sargent County, North Dakota, derives more than half of its $490.8 million GDP from exports. Machinery manufacturing drives the county’s export sector, led by a big Bobcat Company factory.

Meanwhile, Los Angeles County, the nation’s most populous county and home to its busiest port complex, exported $73.8 billion worth of goods and services in 2017 – the most of any county in the nation, but representing less than 10% of its total GDP.

Overall, exports represented 12.1% of U.S. GDP in 2017, according to the Bureau of Economic Analysis. Nearly half of the 3,114 counties and county equivalents in the Brookings dataset (1,533) were at or above that level.

In general, the most export-dependent counties in the U.S. tend to be smaller, less economically diversified, and in the South and Midwest. Of the 50 counties whose exports represent the biggest share of local GDP, 30 are in the South (including 11 in Texas and nine in Louisiana), 17 are in the Midwest, and three are in western states. In fact, only one county in the Northeast – Fulton County, Pennsylvania, headquarters of construction equipment maker JLG Industries – derives as much as 30% of local GDP from exports.

A few populous counties are among the nation’s 50 most export-dependent. Snohomish County, Washington (just north of Seattle), site of an enormous Boeing aircraft assembly plant and home to more than 800,000 people, generated nearly $16 billion in exports in 2017, or more than a third (34%) of its total GDP.

But such places are more the exception than the rule: All but six of the 50 most export-dependent counties in 2017 had populations under 100,000. Three counties in Nebraska that together generated $96 million in exports (nearly all agricultural products), or almost 36% of their combined GDP, had a total population of just 1,892.

Nearly all of the nation’s most export-dependent counties rely on a single industry – or sometimes even a single plant – for the bulk of their exports. In all but eight of those 50 counties, a single industrial sector accounts for more than half of all exports. At the top is Eureka County, Nevada, a gold mining center: $464 million of its $469 million in 2017 total exports came from mining.

More typically, however, manufacturing is the dominant export sector. In 44 of the 50 most-export-dependent counties, the single biggest export generator is some form of manufacturing, with petroleum and coal products (12 counties) and transportation equipment (11 counties) most common.

In the counties where exports have grown the fastest in recent years, one industry – oil and gas – has been overwhelmingly responsible. In 23 of the 30 counties with the highest real export growth rates between 2003 and 2017, oil and gas extraction was the single largest export source. Oil and gas accounted for more than half of all exports in 21 of those counties.

Note: This is an update of a post originally published Oct. 20, 2017.

Counties where exports made up highest share of GDP in 2017

County State Population (2017) Export share of GDP (2017) Biggest export sector St. James Parish LA 21324 67.7% Petroleum & Coal Products St. John the Baptist Parish LA 43339 62.1% Petroleum & Coal Products St. Bernard Parish LA 46108 62.1% Petroleum & Coal Products St. Charles Parish LA 52673 61.3% Petroleum & Coal Products Hancock County KY 8778 56.9% Primary Metal Manufacturing Iberville Parish LA 32920 51.8% Chemical Manufacturing Itawamba County MS 23512 51.8% Primary Metal Manufacturing Sargent County ND 3871 51.4% Machinery Manufacturing Posey County IN 25566 50.8% Chemical Manufacturing Bartholomew County IN 82429 46.4% Machinery Manufacturing Scott County KY 54790 46.3% Transportation Equipment Morris County TX 12381 46.1% Petroleum & Coal Products West Baton Rouge Parish LA 26207 45.3% Petroleum & Coal Products Jefferson County TX 256591 44.3% Petroleum & Coal Products Ralls County MO 10222 42.8% Machinery Manufacturing Hancock County IA 10773 42.5% Machinery Manufacturing Bienville Parish LA 13639 41.1% Petroleum & Coal Products Calhoun County TX 5224 41.0% Chemical Manufacturing Gibson County IN 33622 40.3% Transportation Equipment Edwards County IL 6471 39.7% Transportation Equipment Colbert County AL 54509 39.6% Primary Metal Manufacturing Hunt County TX 93927 39.4% Transportation Equipment Calcasieu Parish LA 202330 39.4% Petroleum & Coal Products Orange County TX 84936 39.2% Chemical Manufacturing Logan County KY 27014 38.9% Primary Metal Manufacturing Calhoun County AR 21770 38.9% Fabricated Metal Products Moore County TX 21878 38.0% Petroleum & Coal Products Iowa County IA 16118 37.6% Machinery Manufacturing Howard County IN 82311 37.2% Transportation Equipment Clay County IN 26155 37.1% Transportation Equipment Talladega County AL 80022 36.7% Transportation Equipment Loup County NE 605 36.7% Agriculture Hutchinson County TX 21362 36.5% Petroleum & Coal Products Eureka County NV 1950 36.1% Mining Galveston County TX 334304 36.0% Petroleum & Coal Products McPherson County NE 494 35.7% Agriculture Keya Paha County NE 793 35.2% Agriculture Washington County AL 16532 35.1% Chemical Manufacturing Ascension Parish LA 123028 35.0% Chemical Manufacturing Choctaw County AL 12935 34.8% Paper Manufacturing Snohomish County WA 803039 34.2% Transportation Equipment Brazoria County TX 362700 34.1% Chemical Manufacturing Carson County TX 6010 33.7% Transportation Equipment Ida County IA 6856 33.6% Machinery Manufacturing Boone County IL 53512 33.5% Transportation Equipment Union County OH 56797 33.5% Transportation Equipment Heard County GA 11759 33.4% Primary Metal Manufacturing Greenlee County AZ 9468 33.3% Mining Harrison County TX 66540 32.8% Chemical Manufacturing Stanton County NE 5977 32.8% Agriculture

Source: Pew Research Center analysis of Brookings Institution data; Census Bureau.