Northern Virginia remains a bastion of traditional, nuclear families at a time when the percentage of married couples with children is plunging across the nation, new census figures show.

About 27 percent of all households in the Virginia suburbs of Washington are married couples with children. Elsewhere in the state, that figure is just 19 percent.

Demographers and experts on family issues say one reason why the region has so many nuclear families is the influx of Hispanic and Asian immigrants, who are much more likely to be part of a traditional family than whites or blacks.

Other factors include Northern Virginia’s high education levels, relative youth and higher income levels, all of which play a role in decisions to marry and have children.

As marriage rates have declined nationwide and the number of unmarried partners with children has soared, researchers say the decision to marry and have children is linked to class and income.

“College-educated young adults have been able to find good jobs, marry and then have children,” said Andrew Cherlin, a Johns Hopkins University sociologist who studies families. “But people with less education have struggled to find jobs in our globalized economy and are much more likely to have children in cohabiting relationships.”

The trends have become increasingly evident in 2010 Census data on household relationships, being released piecemeal this summer.

Virginia’s figures were to be made public Thursday, and similar patterns are expected when statistics for Maryland and the District are released next month.

Virginia is a microcosm of the growing split.

More than a third of Asian and Hispanic households are nuclear families.

Among non-Hispanic white households, just one in five are married couples with children. Blacks had the lowest ratio: one in seven.

But in Northern Virginia, blacks, whites, Asians and Hispanics all accounted for higher numbers of traditional families than their counterparts elsewhere in the state.

The place in Northern Virginia with the highest percentage of nuclear families is South Riding, near Dulles International Airport in Loudoun County and home to many Asian Indian families. More than half of households there are married couples with children.

Both culture and necessity can contribute to the prevalence of nuclear families among Asians and Hispanics, particularly for recent immigrants. Asians have high marriage rates and low divorce rates, and Hispanics tend to have more children, Cherlin noted.

“Both have strong family traditions of staying together,” said Qian Cai, director of demographics at the University of Virginia’s Weldon Cooper Center. “Even if they’re not happy, they stay together. As immigrants, it’s a survival strategy.”

Emma Violand-Sanchez, a member of the Arlington County School Board, notices a distinct difference between the individualism of American culture and the more-communal family values in Hispanic culture.

“We grow up with a concept of we, versus I,” she said. “If you have toys, those toys belong to the entire family, not to one child.

“The majority of us are Catholic, and the church also reinforces the family. Versus living with a partner without getting married, or living independently, away from your family. Family is valued. We grow up with a sense of responsibility to be together.”

Immigrants have helped keep the region’s median age relatively low. The median age in Northern Virginia is under 36, about 21 / 2 years younger than the rest of the state.

“We’re not as old as the rest of the state,” said Lisa Sturtevant, a researcher with George Mason University’s Center for Regional Analysis. “A greater share of the population is in childbearing age.”

Another factor in the number of nuclear families is education, and the Washington region has the nation’s highest proportion of college graduates.

During the past 50 years, the traditional nuclear family has become a reflection of education and income. Roughly nine out of 10 people with college degrees don’t have children until after they marry, Cherlin said.

Conversely, people with high school degrees or dropouts are increasingly having children out of marriage, said Stephanie Coontz, who teaches family studies at Evergreen State College in Washington state and is working on a book about the history of marriage.

“It’s not because they don’t value marriage,” she said. “But expectations of relationships are much higher than they used to be. Now women want to know if a man is mature enough to be a good partner. They’re willing to have a child and delay marriage until they are sure.”

Some say it’s time to reconsider the very concept of what a nuclear family is. Many people already consider any configuration involving children to be a family, Coontz said.

“I’d like to see ‘nuclear family’ more broadly defined,” said Sally Baird, a member of the Arlington School Board who is open about being gay.

“A kid I know comes from a great, solid family structure who is being raised by an aunt and a grandmother, but it’s tight and it is good and that kid is doing well in school. Why should that kid think that his family is somehow less?”