"Happy 94th Birthday to Pete Seeger, who became immersed in folk music while cataloging songs here," the congressional research library and de facto U.S. national library said in a Twitter post.
Rolling Stone, wishing Seeger a happy 94th, cited an earlier profile in which the magazine called the singer "the living embodiment of the native folk tradition."
Dozens of folk festivals celebrated the singer's birthday with special events and radio stations played his music. Rhode Island's Newport Folk Festival, which had Seeger on its original board of directors in 1959, called Seeger "our inspiration" in its Twitter message.
Fan Monica Roman Gagnier pointed out the singer -- whose songs include "Where Have All the Flowers Gone?" "If I Had a Hammer (The Hammer Song)" and "Turn, Turn, Turn!" -- is to perform a free concert in Beacon, N.Y., May 18 to celebrate the Hudson Valley city's 100th anniversary.
Seeger lives in Beacon.
Seeger -- elected last month to join the American Academy of Arts and Sciences -- is expected to be at June's music and environmental Clearwater Festival in Croton-on-Hudson, N.Y., benefiting the non-profit Hudson River Sloop Clearwater environmental organization he and his wife Toshi Seeger founded in 1966.
"Thank you everyone for your birthday wishes," Seeger posted on Facebook, showing a photo of him blowing out the candles of a birthday cake.
Change.org started a petition urging the Norwegian Nobel Committee to give Seeger, a peace, civil rights and environmental activist for more than 50 years, the Nobel Peace Prize.
"Pete Seeger is deserving of the Nobel Peace Prize because of his outstanding career as a cultural messenger for peace and social justice," the website said.
"Using his prowess as a musician and iconic songwriter, he continues to engage people, from all walks of life, from many nations, and across generations, in causes to build peace and create a more civilized world," the site said. "Music is the universal language of peace and no more fitting a candidate is worthy of this honor."