From December 1803 until the spring of 1804, Lewis and Clark used the Old Cahokia Courthouse as a headquarters for collecting information, meeting with territorial leaders, gathering supplies and corresponding with President Thomas Jefferson while the party camped at nearby Camp River Dubois. The courthouse, built as a dwelling in the 1730s, is a unique remnant of the French presence in Illinois. The building became a courthouse in 1793, and for 20 years it served as a center of political activity in the Old Northwest Territory. The building was dismantled in 1901, re-erected twice, and reconstructed on its original site in 1939. It is an excellent example of early French log construction known as poteaux-sur-solle (post-on-sill foundation). The upright hewn logs are seated on a horizontal log sill; the spaces between logs are filled with stone and mortar chinking. The courthouse rests on its original foundation of stone nearly two feet thick. Walnut beams extend the cantilever roof over the porch. Inside are four rooms that originally functioned as a courtroom, a schoolroom, and offices for attorneys and clerks.

Shortly after his arrival in Cahokia, Lewis drafted a letter to Thomas Jefferson describing his experiences and future plans:

Cahokia, December 19th 1803

Dear Sir,

On my arrival at Kaskaskias, I made a selection of a sufficient number of men from the troops of that place to complete my party, and made requisition on the Contractor to cause immediately an adequate deposit of provisions to be made at Cahokia subject to further orders or other destination should circumstances render it necessary. This done, it became important to learn as early as possible the ultimate decision of Colo. Charles Deheau de Lassuse (the Governor of Upper Louisiana) relative to my ascending the Missouri.I determined to loose no time in making this application; with a view therefore of greater expedition, I thought it best to travel by land to St. Louis (the residence of the Govr.).I arrived at Cahokia on the 7th and immediately took occasion to make myself acquainted with Mr. John Hay (the Post Master of this place) and a Mr. Jarrot, in whom from previous information I had every confidence; both these Gentleman are well acquainted with the English & French Languages, a necessary qualification to enable them to serviceable on the present occasion as the Spanish Commandant cannot speak the English Language, and I am unfortunately equally ignorant of that of the French - these gentlemen readily consented to accompany me, and on the next day (the 8th) I set out in company with them to visit Colo. Lasuse.he was sensible the objects of the Government of the U. States as well as my own were no other than those stated in my Passports or expressed by myself; that these in their execution, would not be injurious to his royal master, the King of Spain, nor would they in his opinion be detrimental to his Majesty's subjects with whose interests he was at the moment particularly charged, that as an individual he viewed it as a hazardous enterprize, but wished it every success.he would if permitted by me take a transcript of my Passports, and send them immediately by an express to New Orleans to the Govr. Genl. of the Province, and that he would with cheerfulness give the aid of his influence with that officer, to promote my wishes; and finally as a friend advised my remaining at Cahokia untill the next spring, alledging that by that time he had no doubt the Govrs. consent would be obtained.Thus defeated in my application, tho' not much disappointed nor at all diverted from my future views, I spent the evening with the Commandant and returned the next day to join Capt. Clark who had just arrived at Cahokia. On the evening of the 10th Inst. we left Cahokia, and continued our route up the Mississippi four miles, opposite St. Louis where we remained for the night. Early the next morning Capt. Clark continuted his route with the party to the river Dubois (distant from St. Louis 18 miles) in order to erect cabins for our winter residence.I passed over to St. Louis with a view to obtain from the inhabitants such information as I might consider usefull to the Government, or such as might be usefull to me in my further prosecution of my voyage. I have the honor to be with much respect Your Obt. Servt.

Meriwether Lewis Capt.
1st U.S. Regt. Infty.
(Jackson 1962, 145-147)

During the months of their encampment near Cahokia, the Corps of Discovery was able to comprehensively plan the expedition. Extensive geographic information was compiled, gifts were packaged and organized based on intelligence gathered of the American Indian tribes they would meet, important items were evenly distributed and food was prepared and packaged. Lewis and Clark also made many trips to St. Louis, including March 9, 1804, when Lewis was present at a special ceremony, during which the Upper Louisiana Territory was transferred to the United States. Finally in May 1804, the Corps of Discovery broke camp and proceeded to St. Louis and then on to St. Charles to begin their westward journey.

The Old Cahokia Courthouse is located at 107 Elm St. in Cahokia, Illinois. Tours are conducted Tuesday-Saturday from 8:30am to 5:00pm. Please call 888-666-8624 or visit the website for further information.