In 2012, nearly one in three mothers, or 29 percent, did not work outside the home, up from 23 percent in 1999, said the study from the Washington-based Pew Research Center.
Most of the homemakers, 85 percent, indicated they stayed at home to look after their children. However, six percent said they did so because they could not find employment -- up from one percent in 2000.
A third of stay-at-home mothers were of foreign origin, well above the one in five immigrant mothers in the workforce, something the study said could be attributed to a fast-growing Asian and Latino population.
In addition, stay-at-home moms were more likely to be younger and less educated. A third lived below the poverty line, double the proportion in 1970, compared to 12 percent of working mothers.
More and more were single mothers, while those who were married with a working husband were by far more affluent and better educated.
Sixty percent of Americans surveyed thought it was better for a child for one parent to be at home -- a view most strongly felt among Latinos, Protestants and those with lower levels of education.