The Great Recession ended in 2009. Isn’t it about time that 20-somethings start striking it on their own?

Despite the improving job market, 36% of young adults aged 18 to 31 — also known as Millennials — were living in their parents’ homes in 2012, up from 34% in 2009, according to a new Pew Research Center analysis of U.S. Census Bureau data. In fact, Pew finds that it’s the highest share in at least four decades.

“I was surprised by this recent increase. If we look at 1981, 31% of young adults were living in their parents’ households. For 25 to 30 years, there wasn’t much of a change,” said Richard Fry, senior research associate at Pew Research Center and the author of the report. “This is a new increase.”

Mr. Fry named some contributing economic and social factors to account for the increase in young adults living with mom and dad. Millennials are still having trouble finding their footing in the job market since the financial crisis. A larger share have been putting off entering the real word altogether by enrolling in school. And, an increasing share has been postponing major life events, such as marriage. “I think these three basic factors, particularly job holdings, are important,” said Mr. Fry.