And the number of same-sex couples in the state is growing, the study found, jumping from just under 19,000 in 2000 to nearly 30,700 by 2005.

The "Census Snapshot" of Ohio -- compiled by the Williams Institute at the University of California, Los Angeles -- adds limited commentary to data distilled from the 2000 census and more-recent census updates. Researcher Adam Romero said he hopes the data will better inform debate about related legislation in Ohio.

But Romero and the report stress a regular message of the gay community -- that same-sex couples are mostly similar to married ones, aside from their sexual orientation.

Romero said the main difference highlighted in the report -- of same-sex parents having less income than married ones -- shows the need for same-sex couples to be allowed to marry so they can share and transfer benefits to their children.

"These people are working and paying taxes and ought to be treated equally under the law," Romero said.

David Miller, vice president of Citizens for Community Values, the group that backed the 2004 state constitutional amendment banning gay marriage, said the study tries to gain attention for a cause with only limited, and flawed, information.

"They're trying to create some kind of study that says gays and lesbians are everywhere," Miller said.

The Williams Institute, created to look at sexual-orientation issues, started issuing reports for each state last year and expects to finish in the next six weeks.

The report's findings include:

Ohio had 335,110 gay, lesbian and bisexual people as of 2005.

Same-sex couples make up 0.4 percent of all households in Ohio.

Cuyahoga County had 0.47 percent of same-sex couples. Franklin County, which includes Columbus, had the highest rate, at 0.74 percent.

Individuals in same-sex couples are more likely to have a college degree than those in marriages -- 34 percent to 23 percent.

Same-sex parents make less money than married parents, with median incomes of $45,300 compared with $60,200.

Lynne Bowman, executive director of Equality Ohio, said she believes the counts of gay people and same-sex couples are too low because people remain intimidated to report their situation.

Miller, though, said the report contradicts itself. How can better-educated couples with both partners working not out-earn less-educated single-earner married couples? And he said it contradicts previous estimates of a sizable lesbian, gay, bisexual and transgender population.

"Why is it less than 1 percent in all these counties?" he asked.