According to Michael Hart, the founder of Project Gutenberg, the U.S. Declaration of Independence was the first document posted by Project Gutenberg. Hart entered the text of the Declaration of Independence on a Xerox Sigma V mainframe computer at the University of Illinois' Materials Research Lab in 1971.
The University of Illinois' Xerox Sigma V mainframe computer was one of ARPANET's 15 nodes, forming part of what would eventually become the Internet. "When we started, the files had to be very small as a normal 300 page book took one meg of space which no one in 1971 could be expected to have (in general)," wrote Hart. "So doing the U.S. Declaration of Independence (only 5K) seemed the best place to start." After the Declaration of Independence, the next documents to be posted to Project Gutenberg included the Bill of Rights, the U.S. Constitution, the Bible and Shakespeare's works.