He received the document prior to leaving the university in 1796 to assist the astronomer Andrew Ellicott with determining the Southern boundary of the United States after the 1795 Treaty of San Lorenzo with Spain.
Gillespie became the first person to receive a certificate in his name "in the nature of a diploma" by the university before he left to be the assistant to the secretary, Andrew Ellicott, on the commission to determine the Southern[9] and Western boundary of the United States with Spanish Florida and Louisiana.
Mr. Gillespie, being about to leave the University to attend Mr. Ellicott in determining the Southern boundary of the United States, we have thought proper to give him this certificate.
[16] A letter written by the Secretary of State, Timothy Pickering, to Ellicott about Freeman's conduct mentions his actions were considered "wholly unwarrantable".
[18] The survey encountered some difficulties with the Native Americans, namely the Eufala, the Seminole, and the Upper Creek, and Ellicott at times feared for Gillespie's safety in some of his writings.
[13] In one letter to Ellicott, Gillespie mentioned that Miccosukee warriors under their king, "a man of violent passions", had set out on July 4, 1799, to stop the surveyors.
[10][20] After his United States Survey of the Coast Service, he was a member of the North Carolina House of Commons and represented Bladen County[21] in 1807[22] and during the War of 1812, from 1812 to 1813.
[20][30] One of his daughters, Elizabeth (also known as Eliza),[2] at the age of 14 married John A. Robeson, a descendant of Col. William Bartram, the uncle of the naturalist.
[10] A letter, fragments of legal documents, and a list of accounts written by Gillespie can be found at the Dolph Briscoe Center for American History on the campus of the University of Texas at Austin.