HELENA, Mont. (AP) – As candidates work to get out the vote for Tuesday’s primary election, more than a fifth of Montana’s registered voters have already cast ballots.

As of Thursday, more than 141,000 of the state’s 646,000 registered voters had submitted their absentee ballots, according to the Secretary of State’s Office.

Over the years, the number of early voters has been on the rise. In the 2014 primary, 67.9 percent of all votes cast were absentee ballots amid some of the lowest turnouts in recent years.

In Yellowstone County, the state’s largest, nearly 31,000 of the 49,000 absentee ballots had already been returned. In Lewis and Clark County, nearly 63 percent of the more than 16,000 absentee ballots sent out had been submitted. In Missoula and Gallatin counties, more than half of absentee ballots had been returned.

More absentee ballots were expected to arrive over the next few days, but Secretary of State Linda McCulloch warned that absentee ballots received after Tuesday – even if mailed ahead of the primary – won’t be counted. Those still holding on to their absentee ballots can drop off their completed ballots at their county elections office.

To help boost voting among Native Americans, the Secretary of State’s Office has helped counties establish 13 satellite elections offices across tribal lands. But McCulloch, who recently visited six of those facilities, said foot traffic appeared low.

Despite high-profile contests for president, the U.S. House, governor and four other statewide offices, McCulloch said it was hard to predict what the turnout for Tuesday’s election will be.

Turnout for the primary is usually lower than for the November general election, but elections officials had hoped that the heated contests over the Republican and Democratic presidential primaries would draw more people to the ballot box.

But Donald Trump is now the presumptive Republican nominee and Democrat Hillary Clinton appears to be on the verge of clinching her party’s nomination.

The most contentious battles are occurring in down-ticket legislative matchups between Republican moderates and conservatives.