The cause of death was not immediately known.
Through the EFF, Barlow championed net neutrality and an open internet, often suing the federal government over its handling of online information and privacy matters. She said Barlow understood that "new technology could create and empower evil as much as it could create and empower good" and he made a conscious decision to focus on the latter.
Barlow and Weir met as teenagers and formed a lifelong friendship that took on a new level once Weir joined the Grateful Dead.
Barlow was a lyricist who contributed to many Grateful Dead songs from 1971 until the group disbanded in 1995 following the death of frontman Jerry Garcia.
"He's one of the very first people who recognized the internet was going to be important because it would help people connect in a way they couldn't in the physical world", said Cindy Cohn, the EFF's executive director.
A Wyoming native, Barlow brought together both the counter-cultural and libertarian strains in early internet ideology. The principles lay out Barlow's approach to life in 25 concise bullet points, including "expand your sense of the possible", "live memorably", and "endure".
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Barlow was born in Sublette County, Wyoming, on October 3, 1947.
Barlow was a writer as well as an activist, and he founded the Freedom of the Press Foundation. "John Perry Barlow, he set the bar high, with big boots to follow, and many will try, but no one will ever come close to the guy, for this grateful and graceful guru was one of a kind.".
In a 1996 manifesto, the Declaration of the Independence of Cyberspace, he argued that the U.S. and other governments shouldn't impose their sovereignty on the "global social space we are building".
It proclaimed: "Governments of the Industrial World, you tired giants of flesh and steel, I come from Cyberspace, the new home of Mind".
Barlow is survived by his wife Elaine and their three daughters.