(Bloomberg News) U.S. families without bank accounts grew by 821,000 from 2009 to 2011, pushing the so-called unbanked population to 8.2 percent of the nation's households, according to the Federal Deposit Insurance Corp.

About 17 million adults manage their finances without checking or savings accounts at insured institutions, many of them relying instead on non-bank services such as payday lenders and check-cashing firms, the FDIC said in the National Survey of Unbanked and Underbanked Households released today. The agency released the report in conjunction with a conference to explore ways banks could profit by serving this population.

"Insured financial institutions have an important chance to grow their customer base by expanding opportunities that bring unbanked and underbanked individuals into mainstream banking," Martin J. Gruenberg, the FDIC's acting chairman, said in an e-mailed statement.

The FDIC and consumer advocates have sought to shed light on the unbanked -- those without bank accounts -- and underbanked -- those who rely on alternative services even though they have bank accounts -- as a first step toward promoting use of insured lenders instead of non-bank products, which can have high fees and interest rates.

The study, conducted in 2011, revealed that 8.2 percent of U.S. households, 1 in 12, are unbanked. That is up 0.6 percentage points from the first study, conducted in 2009.

One in five households, or 20.1 percent, were underbanked in 2011. The underbanked rate is higher than the 2009 rate of 18.2 percent but the FDIC cautioned that the survey methodology was slightly different in the two studies.

Unbanked households vary significantly by ethnicity, according to the 2011 report. Black households were 21.4 percent unbanked, and Hispanics registered a 20.1 percent rate, while American Indians were at 14.5 percent. White and Asian households were at 4 percent and 2.7 percent, respectively.