Updated – About 10 percent of ballots have already been cast in the Nov. 5 election, the Department of State reported Friday.

Some 3.09 million ballots were sent to active registered voters starting on Oct. 15. The department reported that 315,538 already have been returned, about 10.2 percent of that total. Ballots have to be returned by mail or dropped at voting centers no later than 7 p.m. on Nov. 5.

The top issue of the 2013 election is Amendment 66, the proposed $950 million income tax increase for P-12 education. Coloradans never have supported a statewide general tax increase since passage of the Taxpayer’s Bill of Rights required voter approval of tax hikes, and the vote is expected to be close. A66 is expected to have greater support in Democratic-leaning counties than in Republican ones.

Of the ballots already cast, 43.2 percent were from Republican voters, 29.7 percent from Democrats and 26.1 percent by unaffiliated voters.

Among major counties, the percentage of ballots returned is larger in Republican and unaffiliated-leaning counties than it is in more Democratic ones. It’s conventional political wisdom that older voters and GOP voters are likely to send mail ballots earlier than other voters.

Curtis Hubbard, spokesman for the Yes on 66 campaign, said, “It’s very early in the process, but we like what we see and we know it will only get better.”

The chart below gives the early voting stats for the state’s 11 largest counties. (After Mesa County, the next two largest counties have just under 35,000 active voters each.) Light blue shading indicates Democratic-leaning counties, light red GOP ones and lavender indicates counties where unaffiliated voters are the plurality group.
Chart of 2013 early voting by county

See the full list of ballots cast by county here.

The department will be reporting on ballots cast periodically until the election, with the next update scheduled Tuesday.

In the last odd-year election, 2011, about 1.07 million ballots were cast, some 50 percent of active voters. That election also featured a school funding proposal, the unsuccessful Proposition 103. But backers of that plan weren’t as well funded as are A66 supporters, and the campaign wasn’t as high profile.