Colorado election officials cautioned on Tuesday that it’s too late to mail ballots for the June 30 primary and urged voters to use drop boxes and their county’s voting centers instead.

Secretary of State Jena Griswold said in a release that 437 secure drop boxes and 137 in-person voter centers are open throughout the state.

The announcement comes a week before ballots are due in a primary that features top-ticket races in both the Democratic and Republican parties, as well as a couple of contested primaries in minor-party primaries.

County clerks must receive ballots by 7 p.m. on June 30. Voters can find drop box and voter center locations at GoVoteColorado.gov, which also includes links to county election offices and other voting information.

Ballot returns statewide reached 442,017 as of midnight Monday, Griswold’s office said, which amounts to almost 12% of the state’s more than 4 million active, registered voters.

Democrats are voting in higher numbers than Republicans, while unaffiliated voters — who can vote in either major party’s primary — have so far cast about twice as many Democratic ballots as they have Republican ones.

Through midnight Monday, county clerks had logged in 186,571 Democratic ballots and 143,129 Republican ballots, with another 110,872 ballots cast by unaffiliated voters yet to be processed.

According to Tuesday’s report, 37,585 unaffiliated voters whose ballots have been processed have opted to vote in the Democratic primary, and 19,024 have registered their preferences in the Republican primary.

In addition, 1,358 ballots had been cast in the Libertarian primary, and 87 ballots have been cast in the Unity Party’s primary.

The Democratic ballot includes statewide primaries for governor, U.S. Senate, attorney general and secretary of state, while the Republicans’ statewide ballot includes races for governor and attorney general. Democrats are also facing high-profile primaries in several congressional districts, while the GOP has only a single congressional primary in a contested district, and both parties have multiple legislative primaries across the state.

The Libertarian Party’s ballot features just one statewide race, for the office of secretary of state. It’s a closed primary, meaning only voters who were registered as Libertarians when ballots started going out on June 8 can participate.

Unaffiliated voters who want to vote in the Unity Party’s primary to pick its gubernatorial nominee, however, can request that party’s ballot from their county clerk, though if they do, they won’t be able to vote in any other primary. By Monday night’s report, 11 unaffiliated voters had done so.

Older voters are returning ballots at a much higher rate than their younger counterparts, with over 56% of total ballots processed through Monday belonging to voters age 65 and older. Just under 9% of ballots have come from voters younger than 35, according to the report.

Jefferson County has returned the most ballots, followed closely by El Paso County, with Denver and Arapahoe counties not far behind.

Eligible Coloradans can still register to vote and cast a vote in person at their county’s voting centers until 7 p.m. on Election Day.