In a report issued Thursday, the bureau said there were 5.6 million stay-at-home moms in 2007 and almost 25 percent of all U.S. married-couple families had a mom who stayed at home.
"Stay-at-home" describes a parent -- male or female -- who stays home to care for children while a spouse is in the labor force, the bureau said.
Rose Kreider, family demographer with the Census Bureau, said the survey -- titled "America's Families and Living Arrangements: 2007" -- enables the bureau to study trends in "basic household and family composition."
Forty-four percent of stay-at-home mothers were under age 35, compared with 38 percent of mothers in the labor force who were under 35. Twenty-seven percent of stay-at-home mothers were Hispanic, compared with 16 percent of other mothers.
The report also found that the number of Americans who live alone rose from 17 percent in 1970 to 27 percent in 2007, and the average household size declined from 3.1 people 2.6 people during the period.