When Joelle Kelly moved in with Bryan Neff this year, her parents were not on her case to get married.

Just the opposite.

"My parents said that we should live together before getting married," Kelly said. "You never know who someone is until you live together."

Kelly, 30, and Neff, 27, could be a poster couple for a demographic trend revealed in U.S. Census Bureau figures released today.

The numbers of unmarried partner households in Sacramento County – as the census calls them – shot up nearly 35 percent between 2000 and 2010. The highest concentrations are in midtown Sacramento, where Kelly lives.

Whether you call it unmarried partner households, cohabitation or – as Kelly did, in jest – living in sin, more and more couples are skipping or postponing marriage.

There were 30,600 such households in Sacramento County in 2000 and 40,900 in 2010.

A similar hike applies to the four-county Sacramento region – including Yolo, Placer and El Dorado counties.

That increase reflects the area's population growth and changing values – like those of Kelly's parents, who have been married more than 40 years.

"In the past 20 years, the social stigma has disappeared," said Michael Rosenfeld, a Stanford sociologist who studies relationships.

"Young people are much more likely to be cohabiting than to be marrying," he said.

Although census figures don't directly connect the unmarried with the young, the areas with a higher percentage of unmarried partners are also areas where there are more young residents, including midtown, Davis and around Sacramento State.

Census numbers show a particular jump in same-sex partner households.

There was a 48 percent jump in self-reported unmarried gay partner households from 2000 to 2010. About 5,300 of the 7,226 such households in the four-county area were in Sacramento County.

In the past, gay couples may have worried about putting their status accurately on official forms, Rosenfeld said.

Beyond that – especially in the more distant past – same-sex couples may have feared even living together, because of law and social stigma.

"There is less closeted behavior," Rosenfeld said.

The absence of gay marriage is one of the reasons writer Katie McCleary says she and Sacramento City College professor Nicholas Miller have remained "happily unmarried" for 11 years.

"The big reason is we have a lot of friends who are (gay) and they're not allowed to marry," said McCleary, 32.

Their non-union was stigmatized at first, but has become more accepted, she said.

The number of husband-wife couples remains much higher than that of unmarried couples. There were roughly six married couples for every unmarried household in Sacramento and Yolo counties.

The ratio was 9-to-1 married-to-unmarried in El Dorado and Placer counties.

Experts offered other possible factors to consider in the growth in living together.

Although more young couples were already forgoing marriage before the economy went sour, "the recession has only increased the trend," said Bradford Wilcox, director of the National Marriage Project at the University of Virginia.

Kelly and Neff, whose move was partly economic, want to marry eventually, she said.

"Everyone in America basically aspires to marriage eventually," Wilcox said.

But they don't want to repeat the mistakes of the divorce-prone generations before, he said.

Unmarried couples may find freedom and simplicity in defining their own relationships outside marriage, but there are downsides.

"We know that kids who are born in cohabitation relationships … are more likely to see their parents break up by age 5," said Wilcox.

Marriage's enforced commitment also facilitates other investments in a relationship, said Rosenfeld.

That includes things like buying a home or having children – although many, like McCleary and Miller, have done so outside marriage.

Rosenfeld notes "traditional" marriage wasn't that way 200 years ago.

"There wasn't one official way to get married," he said.

At times, common law marriage was common in the United States.

Recent changes leave many uncertain where marriage is headed.

"The college students I talk to spend a lot of time worrying how this is going to work," he said.

© Copyright The Sacramento Bee. All rights reserved.

• Read more articles by Carlos Alcalá

Order Reprint