Pinckney's Treaty, or Treaty of San Lorenzo, signed October 27, 1795, a treaty between the United States and Spain. The United States negotiator was Thomas Pinckney, a special envoy. The border line between East and West Florida (owned by Spain) and the southern boundary of the United States was established. Spain agreed to allow United States citizens the free right of navigation on the Mississippi River and to make New Orleans a duty-free port.