Just over 41 percent of Montana's registered voters cast ballots in Tuesday's primary election.
That's the highest midterm primary turnout rate since 47 percent voted in the June 1994 primary during Democratic President Bill Clinton's first term in office.
Turnout in the last midterm primary in 2014 was 33 percent.
Republican voters chose State Auditor Matt Rosendale to challenge Democratic U.S. Sen. Jon Tester, while Democrats chose former state legislator Kathleen Williams to take on Republican U.S. Rep. Greg Gianforte.
Records from the Secretary of State's Office show Liberty County in north-central Montana had the highest voter turnout at 74.4 percent, while Lewis and Clark County had the highest turnout among the five largest counties at 44.6 percent. Yellowstone County's was nearly 43 percent, while Missoula County's turnout was about 36 percent.
Jeremy Johnson, an associate professor of political science at Carroll College, said the statewide turnout shows there's more excitement around this year's midterms than ones in recent years.
More than 152,400 people voted in the Republican U.S. Senate primary, while about 110,800 voted in the Democratic primary for U.S. House.
Johnson said that though turnout was about 27 percent higher for Republicans than Democrats in those races, the difference in votes cast is common in Montana and doesn't show a spike in support for one party or another.
"Generally in primaries (how many votes are cast for each party is) not as meaningful of a predictor of enthusiasm in November," Johnson said.
Gianforte, who didn't face a primary challenger, pulled in about 16,800 votes fewer than all of the Republican U.S. Senate primary candidates combined.
That kind of voter roll-off could be predictive of voter behavior in November, Johnson said.
"It could potentially be meaningful that there's not as much enthusiasm for Gianforte," Johnson said.
Tester, who was also unopposed, got just shy of 3,000 more votes than all of the U.S. House Democratic primary candidates combined.
The Montana Green Party had a contested U.S. Senate primary ballot Tuesday, won by Steve Kelly.
The Green Party qualified to get candidates on the ballot on the last day possible and is facing two challenges from the Montana Democratic Party, one in court and one in front of the Commissioner of Political Practices, over how it qualified.
The Green Party could pull away more liberal Democrats from voting for Tester in the fall. The Greens received 1,574 votes in their U.S. Senate primary, but Johnson said that number can't be used to make any guesses about November.
"The Green Party could play a role in a very close race as a spoiler but I don't think the Green Party in Montana will ever do as well as Libertarians (who can be seen as taking votes away from Republicans)."
The Associated Press contributed to this report.