The Census Bureau says the number of opposite-sex unmarried couples who shared living arrangements jumped 13 percent this year to 7.5 million. That's compared to a 2 percent decrease between 2008 and 2009.
Demographers say a sluggish job market is a likely factor. Many young adults who first turned to friends and parents for financial help as the recession began may now be leaning on a significant other.
A Census Bureau demographer who reviewed the numbers says newly formed unmarried couples living together were more likely to have one partner unemployed.
The number of same-sex couples living together wasn't statistically different from a 2008 estimate.
The findings come after the Census Bureau reported last week that the U.S. poverty rate jumped in 2009 to 14.3 percent, or 43.6 million people, the highest since 1994.