That brings his total raised this year to about $1.02 million, making him one of the strongest fundraisers in the House thus far.
More than 91 percent of the donors came from within the state, and more than 80 percent were donations of $100 or less. Romanoff said previously that he wouldn't take money from PACs or special interest groups to fund his campaign.
The $500,000 is near even with the $514,000 he raised in the first quarter of the year. That quarter, Coffman brought in about $4,000 less than Romanoff.
But both will need to maintain that pace to prepare for what's expected to be one of the nation's tightest races.
Colorado's 6th district is near evenly divided among Republican, Democratic and independent voters, and while it broke for Republicans in three of the last four presidential races, Obama won the newly redrawn district in 2012.
The former Colorado House Speaker — who in 2010 failed to topple Sen. Michael Bennet (D-Colo.) in a primary challenge — is considered a stronger candidate than 2012's Joe Miklosi, and his entry into the race has given Democrats hope for a pickup this cycle.
Coffman has already been the focus of Democratic attacks and is one of the top 10 targets of House Majority PAC this cycle.