The number of self-identified gay couples in the US has risen from 594,391 to 901,997 in a decade, according to the 2010 census results.

While the form does not ask respondents to identify their sexuality, they can tick a box to say if they are cohabiting with a same-sex partner or spouse.

Gary Gates, a scholar at UCLA’s Williams Institute told the Wall Street Journal: “The increase is too big to be explained by a sudden jump in coupling among gay people.”

Instead he suggested the increase is the result of gay and lesbian couples being more willing to identify themselves as such, particular in the more conservative states.

The number of self-identifying gay couples rose by nearly 90% in Montana, Nevada and West Virginia, while the more liberal states of California, New York and Washington, D.C., saw increases of 40% or less.

The numbers also show the proportion of same-sex couples raising children hasn’t changed much since 2000.

Williams Institute research has also found that about 50,000 same-sex couples have married in Massachusetts, Connecticut, Iowa, Vermont and New Hampshire since 2000.

85,000 same-sex couples have entered into civil unions or domestic partnerships in states which offer gay couples that option: Vermont, California, New Jersey, Oregon, New Hampshire, Washington and Nevada.

These figures mean around 15% of gay relationships in the country have official recognition.

Provincetown, Massachusetts had the highest proportion of same-sex couples in the US: 163 for every 1000 people.