October 14 – Lewis arrives at His aunts house with 100 other men[3] to meet with Clark and plan for the expedition.[4]
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May 14 – The Corps of Discovery departs Camp Dubois (Camp Wood) at 4 P.M., marking the beginning of their voyage to the Pacific Coast.
May 14 – The Corps of Discovery arrives at St. Charles, Missouri.
May 14 – Departure from St. Louis
May 16 - Party contains 31 members, mostly US Army personnel including captains, sergeants, and privates.[5]
May 24 – Pass Boones Settlement. Home of woodsman L. Willenborg
May 25 – The expedition passes the small village of La Charrette on the Missouri River. Charles Floyd the men was Pierre Dorion, Jr.-who knew George Rogers Clark. Lewis and Clark persuade Dorion to return to Sioux camp to act as interpreter.
June 26 – The expedition arrives at Kaw Point where the Kansas River drains into the Missouri River basin.
June 28–29 – First trial in new territory. Pvt. John Collins is on guard duty and breaks into the supplies and gets drunk. Collins invites Pvt. Hugh Hall to drink also. Collins receives 100 lashes, Hall receives 50 lashes.
July 4 – Marking Independence Day, the expedition names Independence Creek located near Atchison, Kansas.
July 11–12 – Second trial in new territory. Pvt. Alexander Hamilton Willard is on guard duty. Is charged with lying down and sleeping at his post whilst a sentinel. Punishable by death. He receives "one hundred lashes, each day for four days." (p. 150, 'Undaunted Courage,' Stephen E. Ambrose)
July 21 – Reaches the Platte River, 640 miles from St Louis. Entering Sioux Territory.
August 1 – Captain William Clark's 34th birthday.
August 3 – The Corps of Discovery holds the first official council between representatives of the United States and the Oto and Missouri Indians at Council Bluffs, Iowa. They hand out peace medals, 15-star flags and other gifts, parade men and show off technology.
August 4 – Moses Reed said he was returning to a previous camp to retrieve a knife but he was actually returning to St. Louis (deserting).
August 18 – George Drouillard returns to camp with Reed and Otos' Chief Little Thief. Reed is sentenced to run the gauntlet (approximately 50 lashes) and is discharged from the permanent party.
August 18 – Captain Meriwether Lewis's 30th birthday.
August 20 – Sergeant Charles Floyd dies. He dies from a burst appendix. He is the only member lost during the expedition.
August 23 – Pvt. Joseph Field kills the first bison.
August 26 – Pvt. Patrick Gass is elected to Sergeant. The first election in the new territory west of Mississippi River. George Shannon is selected to get the horses back from Indians.
August 30 – A friendly council with the Yankton Sioux held. According to a legend, Lewis wraps a newborn baby in a United States flag and declares him "an American."
September 4 – Reach the mouth of the Niobrara River.
September 7 – The expedition drives a prairie dog out of its den (by pouring water into it) to send back to Jefferson.
September 14 – Hunters kill and describe prairie goat (antelope).
September 25–29 – A band of Lakota Sioux demanded one of the boats as a toll for moving further upriver. They meet with the Sioux. It was a close order drill. Louis and Clark showed the Sioux how to use air guns. They also gave the Sioux gifts of medals, military coats, hats, and tobacco. It was hard to communicate because of language problems. The expeditioners invited the chiefs on board a keelboat, and gave each 1/2 a glass of whiskey. They acted drunk and wanted more. There were two armed confrontations with Sioux. Some of the chiefs slept on the boat, moved upriver to another village, met in a lodge, and held a scalp dance.
October 8–11 – Pass Grand River home of the Arikara Indians 2,000+. Joseph Gravelins trader, lived with Arikara for 13 yrs. Pierre Antoine Tabeau lived in another village was from Quebec.
October 13 – Pvt. John Newman tried for insubordination (who was prompted by Reed) and received 75 lashes. Newman was discarded from the permanent party.
October 24 – Met their first Mandan Chief, Big White. Joseph Gravelins acted as interpreter.
October 24 – Expedition reaches the earth-log villages of the Mandans and the Hidatsas. The captains decide to build Fort Mandan across the river from the main village.
October 26 – Rene Jessaume lived with Mandan for More than 10 years, hired as Mandan interpreter. Hugh McCracken a trader with the North West Company. Francois-Antoine Larocque, Charles MacKenzie also visited L&C.
November– December – Constructed Fort Mandan.
November 2 – Baptiste La Page is hired to replace Newman.
November 5 - The captains meet and hire Toussaint Charbonneau, a French-Canadian fur trapper living among the Hidatsas with his Shoshone wife, Sacagawea.
December 24 – Fort Mandan is considered complete. Expedition moves in for the winter.
