By Laila Kearney

(Reuters) - Nearly half of gay and lesbian couples living together in the United States are married a year after the Supreme Court's decision to legalize same-sex marriage across the country, according to a Gallup study released on Wednesday.

The percentage of married cohabiting same-sex couples, as opposed to couples living together but not married, rose to 49 percent from 38 percent before the ruling, Gallup said.

In a ruling on June 26, 2015, the Supreme Court struck down same-sex marriage bans in the 13 states that still prohibited it.

Gallup estimates about 123,000 same-sex American couples married in the past year, with a higher number of the unions taking place in states that already had legalized same-sex marriages.

In total, 9.6 percent of gay and lesbians Americans are married, compared to 7.9 percent before the ruling, Gallup said.

The percentage of same-sex couples living in a domestic partnership has declined to 10.1 percent from 12.8 percent, it said.

"This indicates that while many unmarried same-sex couples who were living together got married in the past year, many others stopped living together or no longer consider themselves to be domestic partners," Gallup said.

The results are based Gallup interviews conducted during the past year.

(Reporting by Laila Kearney; Editing by Bill Trott)