With just one day remaining to return ballots in Colorado’s primary election, election officials announced on Monday that they’ve received more than 622,000 ballots, with Democrats slightly outpacing Republicans but both lagging their respective turnout rates at the same point in previous cycles.

Through late Sunday night, the Colorado Secretary of State’s Office said county clerks had logged in 622,391 ballots, including 279,896 cast in the Democratic primary and 265,096 in the GOP primary, with 76,443 to be processed.

That’s a turnout rate of roughly 16% of Colorado’s nearly 3.9 million active, registered voters, compared to the 18.5% turnout on the day before the state’s 2022 primary election.

Voters have until 7 p.m. Tuesday to return their mail ballots to county clerks or cast their votes at voting centers. Colorado residents can also register to vote and cast ballots up until the deadline. Find voting information at GoVoteColorado.com.

Colorado’s primary ballot features several hotly contested congressional primaries, as well as legislative and local races.

This year, the only statewide race on the ballot is the election for the University of Colorado’s at-large regent seat. The Democrats are facing a two-way primary for the seat, while the Republican candidate is unopposed.

Unique this year is a special election on the same ballot in the 4th Congressional District to fill the vacancy created when former Republican U.S. Rep. Ken Buck resigned his seat in March.

Under Colorado’s semi-open primary system, unaffiliated voters can vote in either the Democratic or Republican primary. Among ballots received statewide by midnight Sunday, unaffiliated voters had cast 78,265 Democratic ballots and 64,159 Republican ballots, with 76,411 still in process.

The majority of ballots received so far were from voters age 55 and up. Women have been more likely to cast Democratic ballots, while men have been more likely to vote in the Republican primary.

Turnout has been higher than the statewide average in the 4th CD’s special election, with 108,405 ballots received — 20% of the district’s active, registered voters.

Voters have four choices in the district, which covers Douglas County, a sliver of Larimer County and the Eastern Plains: Democrat Trisha Calverese, Republican Greg Lopez, Libertarian Hannah Goodman and Approval Voting Party nominee Frank Attwood.

Voting centers opened in the 4th CD on June 10 — a week ahead of the rest of the state — to provide extra time to vote in person for the special election. Unlike in the state’s primary election, special election ballots went to every registered voter, including members of Colorado’s minor political parties.

Four of Colorado’s eight congressional districts feature contested primaries.

Six Republicans are running in the 4th CD for the chance to fill Buck’s seat next year: U.S. Rep. Lauren Boebert, Deborah Flora, state Rep. Mike Lynch of Wellington, former state Sen. Jerry Sonnenberg of Logan County, state Rep. Richard Holtorf of Akron and Peter Yu.

Three Democrats are also running in the district — in addition to Calvarese, the party’s nominee in the special election. They are Ike McCorkle, who lost the last two elections to Buck, and John Padora.

On the Western Slope, the 3rd Congressional District also features a six-way Republican contest between Stephen Varela, Jeff Hurd, Russ Andrews, Lew Webb, former state Rep. Ron Hanks, formerly of Cañon City, and Curtis McCrackin. Democrat Adam Frisch is running unopposed for his party’s nomination.

Two Republicans are vying for the nomination in the 5th Congressional District, whose boundaries nearly coincide with El Paso County: former state Rep. Dave Williams of Colorado Springs, the chairman of the Colorado Republican Party, and Jeff Crank. Two Democrats — River Gassen and Joe Reagan — are also running for the seat held by retiring Republican U.S. Rep. Doug Lamborn.

In the northern Front Range’s battleground 8th Congressional District, the GOP primary pits state Rep. Gabe Evans of Fort Lupton against former state Rep. Janak Joshi, formerly of Colorado Springs, for the chance to challenge first-term Democratic U.S. Rep. Yadira Caraveo.

More than a dozen legislative primaries are also in the spotlight this year, including two Democratic primaries in Denver that could help define the party’s profile next year in the Colorado General Assembly.

In House District 4, state Rep. Tim Hernández, who was appointed to the seat by a vacancy committee last summer, is facing a challenge by retired appellate judge Cecilia Espenoza.

In House District 6, Sean Camacho is challenging state Rep. Elisabeth Epps. Epps, who has routinely clashed with the chamber’s leaders.

Both districts are safe Democratic seats, so the winner of the primary will almost certainly determine who takes office in January.

In Senate District 19, the primary to replace term-limited Democratic state Sen. Rachel Zenzinger is heating up between Obi Ezeadi, a Westminster City Council member, and state Rep. Lindsay Daugherty of Arvada.

Reporter Ernest Luning contributed to this article.