The Census Bureau, which struggles to keep up with the rapid changes in American life, is about to start categorizing same-sex married couples as families.

The 2013 American Community Survey results, which will be reported in September, will mark the first time the census integrates an estimated 180,000 same-sex married couples with statistics concerning the nation’s 56 million families. Until now, they had been categorized as unmarried partners, even when couples reported themselves as spouses.

Because of the large disparity between the number of gay and straight married households, combining the two is not expected to have a significant effect on the statistics that scholars and planners use to analyze how families are changing. Its significance is largely symbolic of the growing acceptance of gays in American society.

“I think the American public already thinks same-sex married couples are families, and the Census Bureau is just catching up with public opinion,” said Andrew J. Cherlin, a sociologist at Johns Hopkins University who studies families.

The Supreme Court’s decision in 2013 in United States v. Windsor, which struck down the Defense of Marriage Act, paved the way for the census to change the way it tracks same-sex households after years of discussions about doing so.

Windsor didn’t obligate us to do anything,” said Rose Kreider, chief of the fertility and family statistics branch of the Census Bureau. “But it in some ways made it easier to say: It’s legally recognized federally, so it’s time for us to throw them in with all married couples.”

Same-sex couples have been counted for almost a decade, but the statistics have not been included as part of the data on families. Instead, they have been segregated.

The Census Bureau is continually reassessing the questions it asks and how it phrases them. For example, it is considering a combined race and ethnicity question because many Hispanics are confused about how to identify themselves racially.

Typically, the Census Bureau undertakes years of consultation and testing before it adds or alters the wording of a question. Its attention to detail means that changes often come years after they have become a familiar part of the culture.

Kreider noted that the census didn’t account for unmarried couples living together in a separate category until 1990.

“Given the changes in living arrangements, we probably could have used that category in 1970,” she said. “The legalization of same-sex marriage is fairly recent. You can never say a bureaucracy moves quickly, but we’re not as far behind as we could be.”

The Census Bureau started collecting data on same-sex couples when the unmarried partner category was added in 1990. Although legalizing same-sex marriage was more than a decade away, some people of the same gender said they were married. Because that was not legally possible, the census unilaterally changed the sex of one partner.

The 2000 Census categorized all same-sex households as unmarried partners, regardless of whether the couples said they were married.

Efforts to count the relatively small slice of same-sex couples who are married have been beset by accuracy problems. Following the 2010 Census, statisticians reduced the estimate of same-sex married couples by 28 percent after concluding that more straight couples had mismarked the gender categories. The census adjusted the results by looking at first names and changing the gender when there was a 95 percent chance of a mistake.

“While I fully endorse this change, because it’s the right thing to do, we’re not completely sure how reliable the data will be to start,” said Gary Gates, who studies gay demographics at the Williams Institute at the University of California at Los Angeles Law School. “But on the social and cultural side, it’s important to tell researchers and the public that the federal government views these people as families and these couples as married. That in itself has utility.”

Census officials hope the accuracy will be improved by the 2020 Census. They are testing questions that they hope to introduce in surveys — but not until 2016. People will be given four explicit options to check about their relationship — opposite-sex spouses, opposite-sex unmarried partners, same-sex spouses or same-sex partners. They also will be asked whether they are in a registered domestic partnership or a civil union.

“We’re trying to make changes that reflect what’s happening with American families,” Kreider said. “We’ve been working on it for some years, and we’re continuing to work on it to improve the measurement of American families and emerging family forms.”