Some 131,729 same-sex couples checked "husband" or "wife" boxes on their decennial census forms, the first time people could do so, after gay marriage became legal in Massachusetts starting in 2004.
That 2010 tally of married gay couples is higher than the actual number of legal marriages, civil unions and domestic partnerships in the U.S. Even after New York legalized gay marriage in June, a Census Bureau consultant, Gary Gates of UCLA, put the actual number of legally recognized gay partnerships at 100,000.
"There's no dispute the same-sex population increases from 2000 and 2010," said Martin O'Connell, chief of the fertility and family statistics branch at the Census Bureau. In cases of couples who reported they were living in a marriage relationship, "they basically responded that way because that is truly how they felt they were living."
The total of 646,464 gay couples in the U.S. was a downward revision of the Census Bureau's count of 901,997 released last month. The bureau said Tuesday it had to make the adjustment after determining that coding errors resulted in an exaggerated count for the initial number.
There were also some fairly predictable regional variations in the results:
The highest share of households with reported same-sex couples — both married and unmarried — was in Washington, D.C., at nearly 2 percent. Washington was followed by Vermont, Massachusetts, California, Oregon, Delaware, New Mexico and Washington state. On the other end of the scale, North Dakota, South Dakota and Wyoming had the smallest shares, each with less than one-third of 1 percent.