By Mary Wisniewski

CHICAGO (Reuters) - Nearly 10 million more Americans have fallen into poverty since the 2007-2009 U.S. recession began, and the number is expected to increase due to the slow pace of the economic recovery, a study released on Wednesday by Indiana University showed.

The number of Americans living in poverty grew to 46.2 million in 2010, up 27 percent from 36.5 million in 2006, the year before the start of the recession, the study found. During the same period, the U.S. population increased 3.3 percent.

The U.S. population is roughly 310 million people.

Poverty is defined in the United States as income below $22,113 a year for a family of four.

The study uses 2010 U.S. Census Bureau data released last year plus other government numbers.

Poverty was expected to have increased again in 2011 due to the slow pace of the economic recovery, the persistent high rate of unemployment, and the long duration of spells of unemployment, the study found.

Although the official U.S. rate of unemployment is declining, this is largely due to many adults giving up looking for a job, the report said. The ratio of employed people to working-age adults has improved only slightly since the recession ended in June 2009, the study found.

If the long-term jobless lose their unemployment insurance benefits before the economy produces enough well-paying jobs, the ranks of the "new poor" will continue to swell steadily through 2017, the study found.

(Reporting By Mary Wisniewski; Editing by Daniel Trotta and Will Dunham)