More than 460,000 votes remain to be counted statewide, according to an Arizona Republic tally of ballots outstanding in Arizona counties as of 7 p.m. Thursday.

The remaining ballots could swing major races including the U.S. Senate contest between Martha McSally and Kyrsten Sinema, as well as the Arizona superintendent of schools, and secretary of state races.

Those votes will also push turnout to nearly 65 percent — if all the votes are counted — the highest for a midterm election in recent Arizona history.

According to officials:

Maricopa County has 345,000 ballots to be counted. That includes 150,000 early ballots received before Election Day and 195,000 ballots that were either early ballots dropped off on Election Day, provisional ballots, or out-of-precinct ballots cast on Election Day.

has 345,000 ballots to be counted. That includes 150,000 early ballots received before Election Day and 195,000 ballots that were either early ballots dropped off on Election Day, provisional ballots, or out-of-precinct ballots cast on Election Day. Pima County has 54,000 votes to be counted. This includes about 36,000 early ballots and 18,000 provisional votes. Pima County Registrar of Voters Chris Roads said the Recorder's Office will begin processing provisional ballots Friday morning.

has 54,000 votes to be counted. This includes about 36,000 early ballots and 18,000 provisional votes. Pima County Registrar of Voters Chris Roads said the Recorder's Office will begin processing provisional ballots Friday morning. Pinal County has an estimated 31,800 early ballots still to count, said Michele Forney, elections director. There are 6,800 provisionals left to count, she said, plus about 25,000 early ballots.

has an estimated 31,800 early ballots still to count, said Michele Forney, elections director. There are 6,800 provisionals left to count, she said, plus about 25,000 early ballots. Coconino County has about 10,600 votes left to count, per the elections department there. Those votes won't get counted until Friday.

has about 10,600 votes left to count, per the elections department there. Those votes won't get counted until Friday. Ballots remaining to be counted in the rest of the state total 4,600 in Apache County, 1,700 in Cochise County, 580 in La Paz, an estimated 8,000 in Mohave County, 4,000 in Navajo County, 2,200 in Santa Cruz County, 6,100 in Yavapai County and 3,100 in Yuma County, according to Garrett Archer of the Secretary of State's office.

Heading into Election Day, Republicans outpaced Democrats in returning mail ballots by 7.5 percentage points, according to the Arizona Secretary of State's Office.

Republicans had an even larger cushion at the start of early voting, but Democrats closed the gap as early voting drew to a close, making it the smallest Republican lead in returned ballots in recent election history for midterms.

MORE:Here's why there are still so many votes left to count in Arizona

Maricopa County won't update its vote tally until 5 p.m. Friday. Other counties have been updating vote totals later in the day as well.

The Arizona Republic had projected about 2.18 million voters, or 58.6 percent of those registered, would cast a ballot this election, with a high estimate of 61 percent. But the current numbers could push total ballots cast to about 2.4 million, which is nearly 65 percent turnout.

That would be the most votes cast in a midterm election in recent state history. It could also nearly top the all-time turnout for a midterm election in Arizona, which is 65.1 percent in 1982, Archer said.

The highest voter turnout for a midterm since 1998 was in 2006 when 60.5 percent of voters cast ballots.

Here are the midterm turnout percentages since 1998: