Oregonians are on track to cast more than 1 million votes in a primary election for only the second time in state history, Secretary of State Jeanne Atkins said Monday.

More than 100,000 ballots poured in over the weekend, Atkins said. That put voter turnout rates just above 29 percent overall, with 673,000 votes cast.

That means registered Oregon voters have to turn in 327,000 ballots in just two days -- Monday and Tuesday -- to match 2008's 1 million primary voter mark.

That many ballots could swamp some county elections offices, in a civics-friendly way. But it almost certainly won't match what happened in the 2012 general election, when 436,000 voters turned in their ballot on Election Day.

"Many people still wait until Election Day to turn in their ballot. That's okay," Atkins said in a statement. "Just make sure and have a plan to get your ballot in and have your voice heard in this historic election."

Ballots must be received by the county clerk no later than 8 p.m. Tuesday. Postmarks do not count and in almost all cases around the state it is too late to put a ballot in the mail.

Voters can look up their closest official ballot drop box at www.oregonvotes.gov/dropbox. Oregonians can find contact information for their county clerk at www.oregonvotes.gov/counties.

The sky-high turnout in Oregon's 2008 primary was due to competitive races in both major parties but was driven most acutely by Obama-crazed voters wanting a say in the Hillary Clinton-Barack Obama primary show-down.

Non-affiliated voters, who don't get to vote for or against Donald Trump or Hillary Clinton, are far, far less likely to cast ballots in this primary than registered Republicans or Democrats. In 2008, fewer than 30 percent of non-affiliated voters turned in ballots compared with 76 percent of registered Democrats and 56 percent of registered Republicans.

So far, turnout is highest in Grant County, home to the John Day Fossil Beds, where 49 percent of registered voters turned their ballots by this weekend.

Lowest turnout as of this weekend was in Columbia County, where just 25 percent of eligible voters had voted.

The state's three biggest counties, Clackamas, Washington and Multnomah counties, are known for particularly heavy last-day balloting. All three had turnout of 27 percent as of first thing Monday. Elections officials are expecting a huge last-minute surge to raise those rates substantially.

-- Betsy Hammond