PORTLAND, Ore. – Three mornings a week, when Becky Leung gets ready for work, her boyfriend is just getting home from his overnight job. When her mother drops hints about her twin sister's marriage, she laughs it off. And when she thinks about getting married herself, she worries first about her career.

Leung, 27, cohabits in a Portland, Ore., townhome with her boyfriend but has no plans yet to wed, a reflection of the broader cultural shift in the US away from the traditional definition of what it means to be a household.

Data released Thursday by the US Census Bureau shows married couples have found themselves in a new position: They're no longer the majority.

It's a trend that's been creeping along for decades, but in the 2010 Census, married couples represent 48 percent of all households. That's down from 52 percent in the last Census and, for the first time in US history, puts households led by married couples as a plurality.

"I see a lot of people not having the typical 8-to-5 job, or couples where one person is employed and one isn't. There's other priorities before marriage," Leung said.

The flip in the 2010 Census happened in 32 states. In another seven states, less than 51 percent of households were helmed by married couples.

The reason, said Portland State University demographer Charles Rynerson, is twofold: The fast-growing older population is more likely to be divorced or widowed later in life, and 20-somethings are putting off their nuptials for longer stretches.

"People in their 20s are postponing marriage for many reasons, including money," Rynerson said. "We also have an aging population, so there's more people living alone."

Fears of not being able to hang onto a job, a widening labor market for women and a shift away from having kids at a young age have all proved to be a disincentive for people in their 20s and early 30s to join the ranks of the married.

Leung is indicative of that trend. She's got a marketing job in a trendy city, writes a personal blog on living a gluten-free lifestyle and has plans to get married -- eventually.

"I think a lot of people make a mistake of saying, I've got a good job, I'm stable, I'm ready to take the next step," Leung said. "You never know what happens down the road. That's the whole purpose of dating.

"You're not there to just have fun."

The median age for first marriages has climbed steadily since the 1960s, when men got married at about 23 years old, and women at 20. Now, men are waiting until they're 28 and women are holding off until 26.

"Some of that is people coupling but not being married," Rynerson said. "There are not nearly as many people in their 20s who are married as in previous generations."

The data supports that, as the Census Bureau reported last year that opposite-sex unmarried couples living together jumped 13 percent from 2009 to 7.5 million.

We're also living longer, with an average life expectancy of 78 years, nearly a decade longer than in the 1960s.

To reflect the changing attitudes on marriage, the Census Bureau has broadened the definition of family this year to include unmarried couples, such as same-sex partners, as well as foster children who are not related by blood or adoption.

And attitudes on marriage are changing, too. About 39 percent of Americans say marriage is becoming obsolete, according to a Pew Research Center study published in November, up from 28 percent in 1978.

Oregon is about average when it comes to the declining number of households led by married couples, and reflects the larger nationwide trend.

It's also a state that represents much of the ups and downs of the 2000s: There was population growth during the decade from Hispanics, a decline in the state's manufacturing sector and an economy in the central part of the state that was crushed by the crumbling housing market and Great Recession.

The state to buck the declining-marriage trend is Utah, where 61 percent of households are led by married couples. On the opposite side of the spectrum is Louisiana, which has the second-lowest percent of married people heading households. Louisiana State University sociologist Troy Blanchard said rural and urban poverty plays a major role.

"There's a lot of unmarried female householders, a lot of concentrated poverty where they don't have maybe the education or resources that allows for (marriage)," Blanchard said.

A decade ago, only six states and the District of Columbia were approaching the 2010 trend and had less than half of their households led by married couples. Data scheduled to be released later this year will included statistics for same-sex marriages.

Nationwide, Blanchard said, labor markets' gender disparities are beginning to equal out, allowing more women into professions that had been closed to them for decades and pushing down the number of households led by married couples. .

"We're far from stopping," Blanchard said. "Until we see that eradication of the gender barrier, I would anticipate (situations other than marriages) to get higher and higher."