(Wikimedia Commons/Framartin)

(CNSNews.com) - Four decades ago, in the mid-1970s, young American adults--in the 18-to-34 age bracket--were far more likely to be married and living with a spouse than living in their parents’ home.

But that is no longer the case, according to a new study by the U.S. Census Bureau.

“There are now more young people living with their parents than in any other arrangement,” says the Census Bureau study.

“What is more,” says the study, “almost 9 in 10 young people who were living in their parents’ home a year ago are still living there today, making it the most stable living arrangement.”

The Number 1 living arrangement today for Americans in the 18-to-34 age bracket, according to the Census Bureau, is to reside without a spouse in their parents’ home.

That is where you can now find 22.9 million 18-to-34 year olds—compared to the 19.9 million who are married and live with their spouse.

In 1975, according to Census Bureau data, 31.9 million Americans in the 18-to-34 age bracket were married and lived with their spouse.

Back then, this was the most common living arrangement for that age bracket.

Also in 1975, 14.7 million in the 18-to-34 age bracket lived in their parents’ home; 6.1 million lived in an “other” arrangement (including with siblings, grandparents, other relatives, or unrelated roommates); 3.1 million lived alone, and 0.7 million cohabitated with an unmarried partner.

In 2016, according to the Census Bureau, only 19.9 million were married and lived with a spouse—while 22.9 million lived in their parents’ home.

Also in 2016, 15.6 million lived in an “other” arrangement. 9.2 million cohabitated with an unmarried partner, and 5.9 million lived alone.

The Census Bureau counted college students living in a dormitory as living in their parents' home. By contrast, it counted someone as living with a spouse even if they and their spouse still lived with a parent. The category of living with a spouse, the study said, included any “young adult who lives with a spouse, regardless of whether anyone else is present in the household (e.g., parents, roommates, other family members).”

In 1975, when calculated as percentages according to the Census numbers, 57 percent of 18-to-34 year olds lived with a spouse, 26 percent lived in their parents’ home, 11 percent lived in an “other” arrangement, 5 percent lived alone, and 1 percent lived with an unmarried partner.

In 2016, 31 percent lived in their parents’ home, 27 percent lived with their spouse, 21 percent lived in an “other” arrangement, 12 percent lived with an unmarried partner, and 8 percent lived alone.

The rise in young adults living at home coincided with a decline in the economic status of young men.

“More young men are falling to the bottom of the income ladder,” says the Census Bureau study. “In 1975, only 25 percent of men, aged 25 to 34, had incomes of less than $30,000 per year. By 2016, that share rose to 41 percent of young men (incomes for both years are in 2015 dollars).”

“There are now more young women than young men with a college degree, whereas in 1975 educational attainment among young men outpaced that of women,” says the study.

In the last decade, says the study, the pace of change in the living arrangements of young Americans has been rapid--but has not been uniform across the states and regions of the country.

“Within the last 10 years, the breadth and speed of change in living arrangements have been tremendous,” it says. “In 2005, the majority of young people lived independently in their own household (either alone, with a spouse, or an unmarried partner), which was the predominant living arrangement in 35 states. By 2015—just a decade later—only six states had a majority of young people living independently.”

With the exceptions of California and Mississippi, the Top Ten states with the highest percentages of 18-to-34 year olds living with their parents were concentrated along the Atlantic coast. (See chart below). They included: New Jersey (46.9%), Connecticut (41.6%), New York (40.6%) Maryland (38.5%), Florida (38.3%), California (38.1%), Rhode Island (37.1%), Pennsylvania (37.1%), Massachusetts (37.0%) and Mississippi (36.8%).

With the exceptions of Washington and Oregon, the ten states with the lowest percentages of 18-to-34 year olds living with their parents were concentrated in the Midwest and Mountain states.

These included North Dakota (14.1%), South Dakota (19.9%), Wyoming (20.9%), Nebraska (22.7%), Iowa (22.8%), Montana (24.1%), Colorado (24.6%), Kansas (26.0%), Washington (26.6%) and Oklahoma (26.7%), which tied with Oregon (26.7%).

“Why are there geographical differences in young adult living arrangements?” the Census study asks. “For one, local labor and housing markets shape the ability of young people to find good jobs and affordable housing, which in turn affects whether and when they form their own households.”