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America's families changed dramatically during the past 40 years: households are smaller, fewer married couples have children, more people live alone and the number of unmarried cohabiting couples — including those of the same sex — has grown, according to a census report released Tuesday.

Utah is a bit different, a place where the change away from traditional families has been slower, largely because of the dominant Mormon culture. The Beehive State often ranks at the top, or bottom, of categories that measure changing household structure nationally.

"But over time, it is changing here, too, as more diverse people move here from the outside and bring their culture and religion. We are slowly becoming more like the rest of America," said Pam Perlich, senior research economist at the University of Utah.

She adds that Mormons are changing over time, too. "They have fewer children now," she said. "More women are participating in the labor force and higher education. To be a woman who is married, highly educated and still in the labor force may not have been as easy or accepted a few years ago."

The study notes that in 1970, 40.3 percent of all U.S. households were married couples with children younger than age 18. In 2012, that had dropped by half.

In Utah, though, 30.2 percent of all households were made up of married couples with younger children. That is 54 percent higher than the current national average, but below the 1970 national average.

"Utahns are deferring marriage to older ages and are having fewer children" like other Americans, although they have moved more slowly in that direction, said Perlich.

The report notes that average household sizes nationally dropped from 3.1 in 1970 to 2.6 in 2012. In Utah, it was 3.13 in 2011, the biggest in America but trending downward also to about where the rest of the country was in 1970.

"A data signature of Utah is that we have long had the nation's highest fertility rate. But it is down significantly to about 2.5 children per woman in her lifetime," Perlich said. "It was routine a generation ago here to have four or five children per woman."

The study notes that 67 percent of households nationally with children under 18 are now headed by married couples, and the number has been trending lower. "Washington, D.C., had the lowest share (42 percent) while Utah had the highest (79 percent)."

In the mirror-image statistic of households with children headed by single parents, the report said, "States with the smallest shares included Utah (18 percent), Hawaii (20 percent), and Minnesota (20 percent)." The national average is 25.9 percent.

Nationally, 7.3 percent of households with children are now headed by unmarried couples, and that has been trending upward. "States with the lowest percentages included Utah (4 percent), Arkansas (5 percent) and Alabama (5 percent)," according to the study.

Census data estimate that 3.2 percent of all Utah households are headed by opposite-sex unmarried partners, and 0.6 percent are by same-sex partners. The American Community Survey estimates Utah has 4,914 same-sex couples, and 34.4 percent report they consider themselves as married spouses. The report said the nation has an estimated 605,000 same-sex couple households.

About trends in general, study co-author Jonathan Vespa said, "Over the last half-century the trend in the U.S. has been toward smaller households, fewer family and married-couple households with children, and more people living alone."

He added, "Many of these trends reflect a rising age at first marriage and older adults who can live in their own home for longer."

The study noted that the percentage of households consisting of a person living alone climbed from 17 percent in 1970 to 27 percent in 2012. In Utah, that percentage now is 19.8 percent. —

How Utah, U.S. families compare

Percent of all households:

• Married couples with children under age 18: U.S. 19.6%, Utah 30.2%

• Single parents with children under age 18: U.S. 9.3%; Utah 8.2%

• Married couples without children at home: U.S. 29.1%, Utah 30.2%

• People living alone: U.S 27.5%, Utah 19.8%

• Other households: U.S. 14.6%, Utah 11.6%