Cohabitating Couples - Number of

From StatWiki

In 2009 there were 6,661,000 unmarried couples living together (cohabitating) in the United States.

In 2010, there were 7,529,000 million cohabitating couples, a 13% increase.

[edit] Source

Increase in Opposite-sex Cohabitating Couples from 2009 to 2010 in the Annual Social and Economic Supplement to the Current Population Survey, 15 Sep 2010; there is additional data available at the link, like monthly numbers and breakdowns