The number of unbanked households in the U.S. has continued to decline in recent years despite a slowing-down of the economic recovery, the Federal Deposit Insurance Corp. found in itsbiennial survey unbanked and underbanked households.

The agency found that in 2015, only 7% of U.S. households were unbanked – meaning they had no access to a bank account – a 0.7% drop from 2013 and a 1.2% drop from 2011. In 2015, there were also 19.9% underbanked households – those that have access to a bank account, but also use alternative financial services such as money orders, payday loans or rent-to-own services.

FDIC officials said the drop in the unbanked rate was a surprise.

"While economic conditions improved during the four years before the 2015 survey, the drop in the unbanked rate is greater than we would expect from observed changes in the economy during that period," said FDIC Chairman Martin Gruenberg on Thursday as the agency unveiled the survey.

The top reason households gave for not having an account was a lack of funds to place. Out of all unbanked households surveyed, 57.4% cited this as at least one reason they chose to forgo an account; the next top reason, cited by 28.5%, was privacy protection. This was followed by a mistrust of banks (28%) and account fees considered too high (27.7%) and unpredictable (24%).

But regulators said a bank account can be helpful.

"Developing a relationship with a bank helps consumers build assets and create wealth, making them less susceptible to discriminatory or predatory lending practices, and can provide a safety net against unforeseen circumstances," said Gruenberg.

Though mobile and online banking rose during the last few years, teller banking remained strong too.

In 2015, 60.4% of banked households used online banking to access their accounts over the past year – compared to 55.1% in 2013. The proportion of those respondents using mobile banking jumped to 31.9%, from 23.2% over the same time period.

At the same time, 75.5% of these households said they'd used a bank teller to access their accounts over the past year – a figure that remained relatively stable. Bank tellers were a particularly popular means of access among lower-income, less-educated, older and rural households.

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