The cost of the census was originally budgeted at $14.7 billion, with emergency dollars set aside for additional outreach in cases such as a natural disaster, a flu epidemic or a major operational breakdown.
Because such problems were not extensive, the Census Bureau saved money, officials said. The agency, which is a part of the Commerce Department, also reduced costs due to a higher-than-expected mail response rate of 72 percent, as well as quick field work from census takers who visited homes of people who did not reply by mail.
The Census Bureau said it was still conducting checks on the accuracy of its data, which will be used to distribute House seats and more than $400 billion in federal aid. Results will be released beginning in late December.
Threats of a major boycott from conservatives protesting big government and immigrants wary of law enforcement ultimately did little to disrupt the once-a-decade head count. Census officials attributed that in part to targeted advertising in hard-to-count areas of the U.S., as well as partnerships with civic groups to help boost awareness of the count.
The unused money will remain in the U.S. Treasury. Congress will determine how it is spent.
"With proficient management, the cooperation of the American public and a little bit of luck, the census stayed on track with significant cost savings to taxpayers," Commerce Secretary Gary Locke said.
The Census Bureau came under criticism after it spent $2.5 million for Super Bowl advertising that some Republicans derided as ineffective and wasteful. The Commerce Department's inspector general in February also found the agency had paid at least $3 million to census employees who didn't do any work.
But the agency made clear Tuesday that it had since run its operations under budget and on time.
"This is a significant accomplishment and I would like to thank the American public for responding to the census," said Census Bureau director Robert Groves.
The stakes are high. Because the population count is used to distribute House seats every 10 years, many states pushed for all-out government efforts in outreach, particularly for minorities and the poor, who tend to be undercounted.
States such as New York, California, Texas, Arizona and Florida had average or below average mail-in participation rates, putting them in danger of either losing or gaining fewer than expected congressional seats.
On Tuesday, the Census Bureau said it could not comment yet on census accuracy. In recent weeks, roughly 10,000 household interviews had to be redone after two Census Bureau managers in Brooklyn, N.Y., were fired over allegations that they forged questionnaires. The agency also has begun to rely more on questioning neighbors or other third parties when a person couldn't be immediately reached at home, which reduced the cost of follow-up visits.
The Census Bureau said it expects to complete quality-assurance spot-checks of the work by its 565,000 temporary census employees by mid-September.
In recent years, the census has been ballooning in costs, with its budget increasing by roughly $3 billion after glitches forced the Census Bureau in 2008 to scrap the use of handheld computers in door-to-door canvassing and revert to a paper-based follow-up survey.
For future census surveys, Groves has said he wants the bureau to explore the use of Internet questionnaires, as well as reduce costs and eliminate redundancy, possibly by making greater use of administrative records for basic data such as address, birth date and phone number.