One week after ballots started going out in the mail to Colorado’s 3.28 million active registered voters, nearly 38,000 have been returned to election officials, Secretary of State Wayne Williams announced Monday.

The ballots logged so far – in what election officials stressed is a very preliminary report – account for just over 1 percent of active voters, with 15 days remaining before ballots must be received by county clerks at 7 p.m. June 26.

It’s the first election to allow Colorado’s 1.2 million unaffiliated voters to cast a ballot in either the Democratic or Republican primary, and officials and candidates are anxious to find out how many will participate in which primary – but that data could remain a mystery until the votes are counted, officials said.

It’s likely that tens of thousands of ballots have been mailed by voters but not yet delivered to clerks, or were put in drop-off boxes but not yet retrieved, election officials said. Many of the ballots included in Monday’s report were cast by military and overseas voters, whose ballots were mailed out a month ago and have been arriving by return mail for weeks.

By Monday morning, clerks reported receiving 37,661 ballots – including ballots cast at vote centers, received at 24-hour drop-off locations and sent by mail.

Of those, 15,982 were cast by Republicans, 14,737 were cast by Democrats, and 6,942 came from unaffiliated voters, who received both major parties’ primary ballots in the mail but can only vote one of them.

The figures released by the secretary of state don’t indicate how many unaffiliated voters cast Democratic ballots and how many cast Republican ballots. Election officials told Colorado Politics that those numbers probably won’t be available statewide until votes are counted, though some counties might report their totals earlier.

In a release, Williams reminded unaffiliated voters they’ll receive two ballots but can only vote one of them. If unaffiliated voters return both the Democratic and Republican ballot, they’ll both be thrown out, he said.

Colorado voters are facing the most crowded primary ballot in memory, with four candidates from each major party running for governor, as well as contested primaries for state treasurer, attorney general and congressional and legislative seats across the state.

In the 2016 primary, 644,723 voters cast ballots, for a turnout of 21.38 percent – typical for recent primaries. The highest turnout in the last decade was in 2010, when both parties featured hotly contested U.S. Senate primaries. That year, turnout was 32.36 percent, with 774,071 voters casting ballots.

El Paso County voters had returned the most ballots, according to Monday’s report, followed by Arapahoe and Denver counties. Mesa County had the next-highest number of returns.

Election officials cautioned against reading much at all into the initial reports, however, because the counties are all handling ballots differently – some smaller counties haven’t begun processing their ballots, for instance.

Voters can update their registration, check out sample ballots, determine whether to expect a mail ballot and find places to vote in person or where to drop off ballots at www.govotecolorado.com.