On January 18, 1803, President Thomas Jefferson sent this confidential message to Congress seeking a $2,500 appropriation for an expedition to explore the West. The bill was cryptically referred to as “an act for extending the external commerce of the United States” in the House and Senate journals. On February 22, both chambers passed the bill and the Lewis and Clark expedition was funded. It was necessary for this message, and the subsequent appropriations, to be kept secret because the territory being explored was not part of the United States…yet. Of course this all changed later that year when Congress and Jefferson finalized the Louisiana Purchase. The new territory was officially turned over to the United States on December 20, 1803.
On December 20, 1803, William C.C. Claiborne, Governor of the Mississippi Territory and one of the commissioners appointed to take possession of Louisiana from France, participated in the ceremonial exchange of the territory from Spain to France to the United States. Claiborne issued this proclamation in three languages (English, French, and Spanish) to inform the residents of the territory that they would soon become citizens of the United States, and that in the mean time they could enjoy the freedoms and liberty under the protection of the U.S. Constitution.
Proclamation of William C.C. Claiborne, 12/20/1803, HR 8A-D1, Records of the U.S. House of Representatives (ARC 593571)