As Election Day arrived Tuesday, 33 percent of Salt Lake County voters had already cast a ballot by mail.

“Compared to other years, that’s excellent. And we expect a lot more” to vote on Election Day, said Salt Lake County Clerk Sherrie Swensen. “For comparison, in 2016, we had less than a 27 percent turnout in the primary — and it was a statewide primary for both parties. So we’re doing really well this year.”

Polls are open Tuesday from 7 a.m. to 8 p.m.

It is now too late to mail ballots — which by law must be postmarked before Election Day — but they still may be placed in election drop boxes, or left at in-person voting sites. Lists of them are available online at vote.utah.gov. All Utah counties except Carbon and Emery now conduct voting primarily by mail.

The highest profile race on the ballot Tuesday will determine the Republican nominee to replace retiring U.S. Sen. Orrin Hatch. Former GOP presidential nominee Mitt Romney is facing conservative state Rep. Mike Kennedy.

And in a replay of a special election last year in the 3rd Congressional District, freshman Rep. John Curtis faces conservative former state Rep. Chris Herrod.

The primary Tuesday also has 18 legislative races statewide — 15 for Republicans and three for Democrats. Four legislative incumbents are fighting to survive: Sen. Brian Zehnder, R-Holladay, and Reps. Raymond Ward, R-Bountiful; Christine Watkins, R-Price; and Brad Last, R-St. George.

Democrats have two high profile races in Salt Lake City.

One is to replace outspoken retiring Sen. Jim Dabakis. Opponents are Derek Kitchen, a member of the Salt Lake City Council, and Jennifer Plumb, a pediatrician and anti-opioid overdose activist. The other is a four-way race to replace longtime Rep. Rebecca Chavez-Houck. The candidates are Igor Limansky, Jen Dailey-Provost, Jacquelyn Orton and Darin Mann.

A variety of school board and county-level races are also being waged statewide.

Election officials have several tips for those who have yet to vote.

“For those who are not yet registered to vote, or who are not sure, Utah now allows Election Day voter registration,” said Justin Lee, state elections director for Lt. Gov. Spencer Cox.

Swensen said those people must bring a photo ID and proof of their address, such as a bank statement or a utility bill to a polling location to fill out forms and cast a provisional ballot.

Also, voters who are unaffiliated with any party — which amount to 38 percent of all Utah voters — may still vote in the Republican primary, but need to formally join that party by filling out a form at polling locations, Swensen said.

The GOP allows only its party members to participate in its primaries. By law, it is too late for people who are registered as members of other parties to change their affiliation to cast a GOP ballot, but unaffiliated voters may still join it.

The Democratic Party allows anyone — including members of other parties and unaffiliated voters — to participate in its primaries. Swensen said non-Democrats would not have received such ballots in the mail unless they requested them, but may request them for races in their district at Election Day polling places.

Swensen and Lee expect initial election results — from by-mail ballots that have been processed as they have been received— to be posted online shortly after 8 p.m. Statewide results will be available at sltrib.com and electionresults.utah.gov.

More results will be posted in coming days as late-arriving, by-mail ballots are counted. Swensen said the canvass to finalize results in Salt Lake County is scheduled for July 10.