The Washington-based social research institute surveyed nearly 3,000 online adults to learn how Americans are informing themselves in the run-up to next year's presidential election.
Sixty-one per cent of Millennials, aged 18 to 33, said they got their news about politics and government from Facebook, with another 37 per cent tuning in to local television newscasts.
It was the reverse among Baby Boomers, aged 50 to 68, with 60 per cent watching local TV news and 39 per cent favoring the popular social networking website.
"We are only beginning to understand the complex interactions of personal choice, friend networks and algorithms in the social media space," said Pew's director of journalism research Amy Mitchell.
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"As the research continues, these data suggest there are fundamental differences in the ways younger and older generations stay informed about political news," she said in a statement announcing the findings.
The survey, conducted March 19 to April 29, did not include the so-called Silent Generation, aged 69 to 86, due to the large proportion of its members who don't use the Internet, Pew said.
But overall, Millennials expressed less interest in politics overall, with only 26 per cent saying it was one of their three favorite topics of interest.
Among Generation Xers and Baby Boomers, the proportions were 34 and 45 per cent respectively.
The complete study is at www.Pewresearch.Org.