Black voters were the only racial or ethnic group to show an increase in turnout from 2008, when 64.7 percent voted. Voter rates for whites dropped to 64.1 percent from 66.1 percent. Both black and white voters though had higher turnout rates than Hispanics and Asians in 2012, each at 48 percent.

“Blacks have been voting at higher rates, and the Hispanic and Asian populations are growing rapidly, yielding a more diverse electorate,” said Thom File, a sociologist with the Census Bureau, in a statement announcing the report. “Over the last five presidential elections, the share of voters who were racial or ethnic minorities rose from just over one in six in 1996 to more than one in four in 2012.”

The Census report comes as the GOP is launching an effort to broaden the party’s demographic base, after Republican nominee Mitt Romney’s loss to President Obama in 2012. 

An Associated Press analysis released last month also found that black voters had passed white turnout in 2012, and concluded that Romney would have won the race if the racial breakdown of the electorate had mirrored that of the 2004 election.

Lawmakers are also tackling the contentious issue of immigration reform, with a Senate proposal which could legalize the 11 million illegal immigrants, mostly Hispanic, already in the country.

The Census study found that the number of black voters rose between 2008 and 2012 by more than 1.7 million, with the number of Hispanic voters increasing during that period by 1.4 million and Asians by 550,000. By contrast, the number of white voters dropped by 2 million. 

The 2008 and 2012 races, boosted by Obama’s campaigns, mark a rise in black voters turnout since 1996, when the Census first recording election data. Since the 1996 election, the bureau said black turnout rates have risen 13 percentage points. 

Overall, voter turnout of all eligible voters dropped from 63.6 percent in 2008 to 61.8 percent in 2012.