Minnesota is only months away from a historic turning point that it has been sliding toward for decades: the moment when fewer than half of the state’s adults are married.

The gradual erosion has less to do with a rejection of marriage than with economics, changing lifestyles and an aging population.

“Ninety percent of Americans marry by age 45,” said state demographer Susan Brower. “It’s nothing to do with the institution of marriage. It’s an age thing, including the growth in seniors, who are likelier to be widowed.”

U.S. Census data to be released Thursday show just what the change looks like from city to city: The adult population of an aging Arden Hills, for instance, has dropped from 53 percent married to 44 percent in a single decade, creating a new array of household types.

The percentage of married couples across the nation as a whole dropped below the 50 percent mark just after the turn of the century. Minnesota’s high-end demographics give it one of the nation’s highest rates of marriage, but it’s sliding along with the rest of the country.

The state’s marriage rate stood at 53 percent as recently as 2005, but by 2014 it was just a sliver above 50 percent — 50.5. If it keeps eroding at the same rate as it has been lately, the symbolic reversal will happen next year.

The marriage gap

The marriage rate tells us a lot about ourselves, said Mark Mather, a demographer with the Population Reference Bureau in Washington, D.C. At the younger end of the age spectrum, it reflects a more highly educated group of young women who are delaying marriage; it also reveals a class divide.

“The aging of the population is playing a role,” Mather said, “but it’s really what’s happening at both ends of the age spectrum. Young adults with college degrees are delaying marriage but, once married, are staying married. Among those who don’t have degrees, we’re seeing big declines in both getting married and staying married: It’s a pretty big trend, this marriage gap.”

Changing lifestyles play a role, too.

Kate Redpath, who has lived in Mendota Heights since 2009, has noticed “all the children on my block leaving the nest, I guess,” as a sign of time moving on. But she also speaks cheerfully after a yoga class of “my man, my 20-year partner,” with no trip to the altar involved.

The advent of gay marriage in Minnesota is helping to slow the slide, but is overwhelmed by larger forces, demographers say.

Among Minnesota cities, the places with the most married adults tend to be fairly well-to-do suburbs and exurbs: Elko New Market, in southern Scott County, is No. 1 among cities over 2,500 in population, with 78 percent of its adult population married, followed by Carver, Deephaven, North Oaks and Victoria, all over 70 percent, according to census estimates to be made public Thursday.

Places with the fewest married adults tend to be college towns filled with students (Bemidji, Winona, Mankato, St. Cloud, Crookston, Northfield and St. Peter are all under 40 percent) or major urban centers. The percentage of married adults in Minneapolis stands at 33 percent. In St. Paul, it’s 38 percent; in Duluth, it’s 39 percent.

The central cities, though, are holding steady at those levels. Cities where married couples dropped the fastest between the two five-year periods covered by census surveys — 2005-2009 and 2010-2014 — include distant exurbs hard hit by the recession (Chisago City fell from 66 percent of its adults being married to 53 percent), Iron Range cities, and a smattering of aging suburbs, such as Arden Hills and Andover.

Arden Hills happens to be on the verge of transforming a single site almost seven times as big as the sprawling General Mills corporate campus into a new town center aimed at a 21st-century suburban market, with apartments, townhouses and condos within walking distance of shops. It’s a place likely to appeal to singles, whether young unmarrieds or older people whose spouse has died. Only 11.5 of 437 acres at Rice Creek Commons, formerly the Twin Cities Army Ammunition Plant, are planned for larger lots.

“When I get calls from residents about it, the No. 1 inquiry I get is from empty nesters, people who have larger single-family homes and want to downsize to something smaller and maintenance-free,” said Jill Hutmacher, the city’s development chief.

“What’s happening in Arden Hills is not the same as in a St. Michael,” Brower said. “In Arden Hills, it’s the loss of a spouse; in the exurbs it’s likelier to be people leaving because of the recession.”

Still, Minnesota’s rank even now as one of the top spots for marriage can be linked, Brower said, to its relative youthfulness — the states with the lowest rates of marriage include retirement draws such as Florida and Arizona — as well as its prosperity, its high levels of education, and its racial and ethnic makeup.

“We still have a large proportion of non-Hispanic whites, who are likelier than some groups to marry,” Brower said. “And that raises the question, ‘As we become more and more racially and ethnically diverse, might that affect our rates of marriage?’ ”

The answer might depend, she said, on the mix of groups: African immigrants may end up having higher marriage rates than native-born blacks, and in fact a recent rise in black married couples in Minnesota may well be due to those immigrants.

“When we think about marriage, we can look at it from a moral standpoint, but it’s a serious economic issue as well,” Brower said. “It’s harder for lower-income folks to find that stability. A lot of times, too, we’re comparing today’s rates to historic highs in the ’40s or ’50s, when it was in the 70-plus-percent range.

“But if we stretch back further, into the late 1800s, rates of marriage were lower. The apex was midcentury.”