Article Two of the "Treaty of Friendship, Limits, and Navigation Between Spain and The United States" set the boundary between the United States and the Spanish Foridas. It was signed on October 27, 1795, but not ratified until 1796.
"The Southern boundary of the United States which divides their territory from the Spanish Colonies of East and West Florida, shall be designated by a line beginning on the River Mississipi [sic] at the Northermost [sic] part of the thirty first degree of latitude North of the Equator, which from thence shall be drawn due East to the middle of the River Apalachicola or Catahouche, thence along the middle thereof to its junction with the Flint, thence straight to the head of St Mary's River, and thence down the middle there of to the Atlantic Occean."
The northern borders of Florida are still in use today.
Treaty of Friendship, Limits, and Navigation Between Spain and The United States; October 27, 1795 from the Avalon Project
Treaty of Friendship, Limits, and Navigation Between Spain and The United States, October 27, 1795 from HathiTrust
