Jo Soroka didn't need to see the latest census data to believe one of the more jarring findings: that married couples head fewer than half the households in Pennsylvania and the country.

When Soroka opened the Sonrise Christian Day School in Linwood, Delaware County, in 1995, she had only a half-dozen single parents on her rolls. Now more than two-thirds of her clients are single parents.

Soroka recalled the morning two years ago when a boy asked a classmate about the man who had accompanied her and her mother to school. "That's my daddy," the girl said.

"No," the boy shot back. "Daddies don't live with mommies."

Increasingly, he's right, the census found.

The percentage of Pennsylvania households with a husband and wife dropped to 48 in 2010 (from 55 percent two decades ago), matching the national figure, the data show. New Jersey also dropped, and now has 51 percent of households led by married couples.

At the same time, the number of single parents, people living alone or with an unmarried partner, continued to climb.

The trends are pronounced in Philadelphia and other high-density, low-income areas, but the shift is occurring across the region.

The reasons abound: Concerns about money persuade young couples to delay marrying and starting a family and persuade older ones to forgo marriage entirely. Women hesitate to marry a man who can't support a family, or opt to raise children by themselves. For all ages, living with a partner, even a same-sex partner, has grown more culturally acceptable.

"The institution of marriage has changed more rapidly in the past half-century than probably in any time in recorded history," said Frank F. Furstenberg, a University of Pennsylvania professor who studies family trends. "It doesn't have to do with people's desire. Most people say they want to get married. They believe in marriage. They hope they get married; they usually do. But they do it with a lot more caution - and a lot later."

The trend is showing up in parenting classes, on playgrounds, and in courthouses. And it has wider implications. More single parents mean more working parents or sole-income families, traits that shape housing and transportation needs, schools, and child-care services.

Single parents are the most obvious indicator of the trend, but not the only one.

Two-thirds of the five million households in Pennsylvania still describe themselves as families, with at least two relatives living under the same roof, last year's census found. And two-thirds of the households with children younger than 18 are still led by a married couple.

What's different is the rising number of people who live with a partner without marrying or in a family setting that does not include a spouse.

In Philadelphia last year, barely a quarter of the family households, or nearly 170,000, reported that both spouses lived under the same roof. That was about 20,000 fewer than a decade earlier. At the same time, the number of single-parent households citywide climbed to about 83,000.

One is headed by Angela Sutton, 35, a Northeast Philadelphia mother of two boys. She said that she had twice hoped to marry - to the fathers of her sons - but that each time the relationship had dissolved.

Raising her boys alone wasn't what Sutton envisioned, but she said she preferred it to staying in an unhealthy relationship or with a man who couldn't support a family. It was also easy to accept because so many others were doing the same thing.

"I have more single-parent friends than non-single-parent friends," said Sutton, a Drexel University student. "It's everywhere."

Across the region, including South Jersey, single parents lead more than 190,000 families, the new data show. There are 31/2 times as many single mothers as single fathers, but both groups are swelling.

Carson Valley Children's Aid family center in Norristown began offering a parenting class for fathers last year, and a dozen signed up, director Julie O'Connor said. This year, enrollment jumped to 50. About half are single dads.

"It's definitely not the stigma it once was," said Malcolm Bonner, the class teacher.

Those who don't live alone are increasingly choosing to couple with a partner instead of a spouse. The number of Pennsylvanians living with an unmarried partner rose 45 percent last decade, to 332,000. The total in South Jersey rose 26 percent, to 190,383. Nationally, the increase was about 40 percent, to 7.7 million, or a little more than 2 percent of the population.

How many of those are same-sex partners won't be clear until the Census Bureau releases more data this year. Its five-year American Community Survey, released last year, found that barely half of 1 percent of the unmarried partners described themselves as same-sex partners.

The increase in partnering has coincided with a trend toward later marriages, suggesting that couples might live together because it's convenient or cheaper or serves as a trial period before marriage.

It also reflects learned behavior, experts say. The generation now coupling grew up with parents more likely to divorce. They became accustomed to sharing the house with Mom's boyfriend or Dad's girlfriend. They also saw friends and classmates in the same situation.

In the late 1960s, about 11 percent of spouses lived together before taking their vows. "Living in sin" was the popular phrase. These days, more than half of married couples first cohabitate.

"When is the last time you've heard anyone say someone is 'living in sin'?" asked Catherine Cohan, a Pennsylvania State University psychologist who studies marriage trends.

The shifts are also apparent on the other end of the life scale. Family lawyers say more older spouses are separating after decades of marriage and returning to the single life or choosing a partner - options that weren't financially viable or socially acceptable in the past.

Cheryl Young, the chair of the family law section for the Pennsylvania Bar Association, said she had noticed an uptick in older couples, often divorced, who are seeking legal advice on cohabitation.

"Certainly the more nontraditional stuff is getting much more significant," said Young, a Norristown lawyer.

Tiffany Kator of Boothwyn was 8 when her parents divorced in the early 1980s. At the time, she knew almost no other children whose parents lived apart.

Now 35 and married, Kator has three children. Her mother lives with a male partner under a cohabitation agreement. Her oldest child, a 6-year-old girl, has many friends or classmates who live with one parent or their grandparents.

"She's seeing such a variety in households," said Kator, a Widener University administrator. "My children are growing up to see - what they see is family is not what everybody else calls family."

Her children's children may see starker changes.

Furstenberg, the Penn researcher, said he believed marriage might revert to its status from centuries ago - a practice reserved almost exclusively for the rich and noble.

"For the next 10 or 20 years, we're going to see this trend of inequality growing in two types of family systems, one that is more stable, more secure - economically and probably emotionally - among the college-grad-plus" group, he said.

"The people below college are by and large going to have more difficulty forming relationships and marriages - because the economic difficulties that Americans face contribute to the emotional security that can be achieved."

Contact staff writer John P. Martin at 215-854-4774 or jmartin@phillynews.com.