A poll carried out among people aged 18-34 found that 20 percent of respondents identified as lesbian, gay, bisexual, transgender or queer.
The online survey was conducted by Harris Poll among 2,037 adults in November 2016, according to the Miami Herald.
The result showed substantially higher than the findings of other surveys. A Gallup poll in 2015 found that 3.8 percent of the adult population identified as LGBT. Meanwhile, a Centers for Disease Control and Prevention survey in 2013 found 96.6 percent of respondents said they were straight, 1.6 percent identified as gay and 1 percent as bisexual.
Other polls have returned varying results, with between 3.4 and 8 percent of the population identifying as LGBTQ.
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"This report shows a remarkable new era of understanding and acceptance among young people -- an inspiring indication of the future. Though laws can be unwritten, hearts and minds in America have been changed for the better -- and that is a reality less easily unraveled," said Sarah Kate Ellis, president of GLAAD.
The percentage of millennials identifying as LGBTQ was higher than any other age group. In the 34-51 age group, the result was 12 percent, while 7 percent of those aged 52-71 and 5 percent of those over 72 stated they were LGBTQ.
A total of 84 percent of millennials stated they were "strictly heterosexual." This compared with 91 percent or higher among all other age groups.
The large difference between the Harris Poll survey and previous polls could be the result of online polling. A 2015 New York Times article noted how online poling firms face the difficulty of not being able to carry out random sampling as traditional telephone surveys do.
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The results of the Harris poll were released in the aftermath of the U.S. Census Bureau's announcement that it had mistakenly proposed counting the number of LGBTQ people in its 2020 census.
The bureau's plan "inadvertently listed sexual orientation and gender identity as a proposed topic in the appendix," a statement read, according to The Associated Press. "This topic is not being proposed to Congress for the 2020 Census or American Community Survey. The report has been corrected."
Gay rights groups said omitting the sexual orientation and gender identity category would prevent LGBTQ people from accessing some government services.
"They can't address what they can't see. They're making it so there's no information to understand the needs of the LGBT community," Laura Durso, vice-president of the LGBT Research and Communications Project, told AP.