County clerks start sending primary election ballots in the mail to Colorado voters on Monday, kicking off three weeks of voting to designate Republican and Democratic nominees to the November ballot in contested congressional, legislative and local races.

Voters in the state’s 4th Congressional District will also be able to vote — on the same ballot — in the vacancy election to fill the remainder of former U.S. Rep. Ken Buck’s term, following the Republican’s resignation from Congress in March.

Clerks have until Friday to mail out ballots, and voters have until 7 p.m. June 25 to return them or to vote in person at voting centers, which open across the state in coming weeks.

Under Colorado’s semi-open primary system, voters who are registered with one of the state’s two major parties — the Republicans and Democrats — will receive their party’s primary ballot, while unaffiliated voters receive both major parties’ ballots but can only vote and return one of them.

Colorado residents can register to vote, update their information and check their status at GoVoteColorado.gov. The site also includes tools to find ballot drop boxes and local voting centers, as well as links to contact county clerks, who administer the election.

All voters can also sign up at the site to track their ballot using the statewide BallotTrax system, which notifies voters by email or text when their ballots have been mailed, when they’ve been received and when they’ve been accepted.

There’s only one statewide race on the primary ballot this year — the Democratic contest for the at-large seat on the University of Colorado Board of Regents — but both major parties are awaiting decisions in tightly contested congressional and legislative primaries. There are also primaries for district attorney and county offices in some parts of the state.

“Ballots are arriving to your mailbox soon,” Colorado Secretary of State Jena Griswold said in a statement on Monday. “There is still time to register to vote if you have not already, and I encourage every eligible Coloradan to do so.”

Coloradans who have lived in the state for at least 22 days before an election — that’d be Monday for this year’s primary election — can register to vote and cast ballots before polls close, but only voters who have registered or updated their registration information by June 17 will receive a ballot in the mail, the Secretary of State’s Office noted.

There are a few wrinkles in the procedure this year due to the special vacancy election to elect Buck’s replacement in the 4th CD, which covers most of Douglas County, parts of Larimer County and the Eastern Plains.

As usual, voters affiliated with one of Colorado’s officially recognized minor political parties — the Libertarians, Greens and others — won’t receive a primary ballot, but members of minor parties who live in the 4th CD will receive a ballot featuring only that district’s vacancy election.

More than 150 voting centers will be open by June 17, and more than 400 24-hour drop boxes will be operating by June 18, though some locations will open both prior to those dates. Check GoVoteColorado.gov for details.

In the 4th CD, voting centers are set to open earlier — on June 10 — to provide an extra week of early voting in the vacancy election, the Secretary of State’s Office said.