Michael Hart, who was widely credited with creating the first e-book when he typed the Declaration of Independence into a computer on July 4, 1971, and in so doing laid the foundations for Project Gutenberg, the oldest and largest digital library, was found dead on Tuesday at his home in Urbana, Ill. He was 64.

His death was confirmed by Gregory B. Newby, the chief executive and director of Project Gutenberg, who said that the cause had not yet been determined.

Mr. Hart found his life’s mission when the University of Illinois, where he was a student, gave him a user’s account on a Xerox Sigma V mainframe computer at the school’s Materials Research Lab.

Estimating that the computer time in his possession was worth $100 million, Mr. Hart began thinking of a project that might justify that figure. Data processing, the principal application of computers at the time, did not capture his imagination. Information sharing did....