An unusually high number of Democratic absentee ballots in South Dakota's most populated county could indicate a heavy turnout for Tuesday's state primary.

Minnehaha County Auditor Sue Roust said 3,300 absentee ballots had been requested as of Monday and 3,000 had been returned.

But what's most striking in the county, home to Sioux Falls, the state's largest city, is the split. Some 2,300 of those ballots are Democrat and 1,000 are Republican, Roust said.

"It's over two-to-one Democrat to Republican and normally it's more Republican," she said. "That to me is indicative to what kind of turnout we're going to have."

The neck-and-neck race between Democratic presidential candidates Barack Obama and Hillary Rodham Clinton has put South Dakota in a rare spotlight. South Dakota and Montana hold the nation's final two contests of the primary season, and Clinton and Obama and their surrogates have made numerous campaign stops in South Dakota in the weeks leading up to the vote.

In Pennington County, home to Rapid City, 3,608 of the requested 3,997 absentee ballots had been returned as of 5 p.m. Friday, and Lori Severson, the county's election supervisor, said she expected more to come in on Monday. Severson said she did not have a party breakdown of the absentee numbers.

Clinton and Obama will appear on Democratic ballots in Union County, but the main issue there is a Texas company's request to turn nearly 3,300 acres north of Elk Point into a planned development district for the $10 billion oil refinery.

The Hyperion Energy Center, planned for just east of Interstate 29 between state highways 48 and 50, would process 400,000 barrels of thick Canadian crude a day.

As of Friday, 1,594 registered voters had requested absentee ballots and 1,018 had been returned, Union County Auditor Carol Klumper told the Sioux City Journal.