And the uncertain economic times may be to blame.
Last year only 45 percent of Americans ages 25 to 34 were married, down from 55 percent in 2000, and the share of young adults who have never been married shot up to 46 percent from 34 percent over the decade, according to the Census Bureau's latest American Community Survey.
That's the first time the never-married in this age group have outnumbered the married.
The trend appeared to accelerate amid the economic turbulence of recent years, and even among the total population ages 18 years and older, the proportion of married Americans fell to 52 percent last year -- the lowest percentage on record since the census started collecting information on marital status more than a century ago.
"The data suggest that more young couples are delaying marriage or [forgoing] matrimony altogether, likely as an adaptive response to the economic downturn and decline in the housing market," Mark Mather and Diana Lavery of the nonprofit Population Reference Bureau write in an analysis of the census report.
But that doesn't mean Americans are skipping relationships altogether.
The decline in marriage has come at the same time as a sharp rise in the number of people entering cohabitation relationships with opposite-sex partners, as well as partners of the same sex.
Though cohabitation as an alternative or precursor to marriage has been rising since the 1970s, the latest census data links "the recent increase in cohabiting couples to rising unemployment rates and growing economic uncertainty, especially among young men," Mather and Lavery wrote. "Given the scope of the recent recession, many more couples are likely to choose cohabitation over marriage in the coming years."
"Marriage is a big step with lots of financial implications, so it makes sense that some people would postpone getting married until the economy improves," Mather added in a telephone interview. "This is especially true for those with less education and earnings potential."
That link between marriage and education -- and by extension, income -- has also experienced a reversal in historical trends.
Until the 1990s, marriage rates were higher among Americans with just a high school diploma than among Americans with a four-year college education. College-educated men and women were far more likely to put off a trip to the altar.
But over the past decade, the married proportion of young American adults with a high school diploma or less plummeted by 10 percentage points to 44 percent, according to the bureau's Current Population Survey. By 2010, 52 percent of Americans with a bachelor's degree or more in this age group were married, up 4 percentage points over the decade.
Any statistical link between marriage and economic success may be skewed by the Darwinian possibility that women or men with higher potential earning ability and better health are "selected" into marriage.
But Mather and Lavery note that most researchers agree marriage itself has a positive effect on people's well being.
"The recent decline in marriage," they said, "may contribute to worse outcomes for less educated individuals, beyond those resulting from the recent recession."