For the first time in more than 40 years, households consisting of a husband and wife now account for less than half the households in Washington state, new census data show.

For the first time in more than 40 years, households consisting of only a husband and wife now account for fewer than half the households in Washington state, new census data show.

The percentage of married-couple households — with or without children — has been on the decline for years as more people delayed marriage and put off having kids.

In 2010, 49 percent of households in the state were composed of just a married couple, down from 52 percent in 2000. Nuclear-family households — husband and wife with children — dropped to 20 percent from 24.

“Since 1960, husband-and-wife families have declined as a share of all households,” said Richard Morrill, a local demographer and geographer. “Fewer younger families are being formed. We’re seeing more single people coming here — from farmworkers in Eastern Washington to foreign workers at Microsoft.”

Unlimited Digital Access. $1 for 4 weeks.

The findings are included in data released by the Census Bureau on Wednesday. The data add details about age, race, housing and family relationships to an emerging demographic portrait of the nation.

The Census Bureau is doing a state-by-state rollout of the data.

Among other findings for Washington state:

• The ongoing housing crisis, in full swing when census forms were being completed last year, helps explain an increase virtually everywhere in the percentage of households with relatives and unrelated people living under one roof.

• Across the state, from the San Juans to Spokane to Vancouver, the proportion of households where people live alone continued to rise.

• The percentage of households with unmarried partners — both gay and straight — increased virtually everywhere, a reflection not only that more heterosexual people are cohabiting but also that more gay and lesbian couples are identifying themselves as such.

The census for the first time is counting as married all gay and lesbian couples who checked the husband or wife category on their forms last year. Data indicating how many did so won’t be released until summer.

One of the most glaring findings in the current release is the continuing erosion of the nuclear family.

Demographers say this downward trend has been in place nationwide for decades and is evident in those states where demographic data already have been released.

In cities such as Kent, Federal Way and Lynnwood, the percentage of nuclear-family households declined from 10 years ago, while remaining steady in some unexpected places, such as Seattle.

Lornet Turnbull: 206-464-2420