The share of mothers who do not work outside the home rose to 29 percent in 2012, up from 23 percent in 1999, according to a new Pew Research Center analysis of US government data.
The overall rise in the share of US mothers who are foreign born, and rapid growth of the nation's Asian and Latino populations, may account for some of the recent increase in the share of stay-at-home mothers, the analysis said.
The report found that 28 per cent of US children, or 21.1 million Americans younger than 18, were being raised by a stay-at-home mother in 2012, a jump of 4 percentage points from 2000.
Asian and Hispanic children were the most likely to be raised by stay-at-home mothers - 37 per cent and 36 percent - in 2012. That compares with 26 percent of white children and 23 per cent of black children.
The report found that stay-at-home mothers are less likely than working mothers to be white (51 percent are white, compared with 60 per cent of working mothers) and more likely to be immigrants (33 percent vs 20 percent).
The broad category of 'stay-at-home' mothers includes not only mothers who say they are at home in order to care for their families, but also those who are at home because they are unable to find work, are disabled or are enrolled in school, the report said.
The largest share of stay-at-home mothers consists of married stay-at-home moms with working husbands. They made up roughly two-thirds of America's 10.4 million stay-at-home mothers in 2012.
In addition to this group, some stay-at-home mothers are single, cohabiting or married with a husband who does not work.
A growing share of stay-at-home mothers - 6 percent in 2012, compared with 1 per cent in 2000 - said they are home with their children because they cannot find a job.
No matter what their marital status, mothers at home are younger and less educated than working counterparts, the report said.
One of the most striking demographic differences between stay-at-home mothers and working mothers relates to their economic well-being. Fully a third (34 percent) of tay-at-home mothers are living in poverty, compared with 12 per cent of working mothers.
Among at-home mothers living in poverty in 2012, 36 percent were immigrants, the report said.