How long did the expedition go on?

Answer 1

Before Lewis met up with Clark, he began the expedition on August 30, 1803 in Pittsburgh PA. Lt. William Clark would offer to join Lewis on the expedition weeks later on October 13, 1803 at Camp Dubois (in present-day Indiana). From there, they sailed down the Ohio River towards St. Louis. In spring 1805, they continued to the headwaters of the Missouri River, struggled across the Continental Divide, and headed west along the Salmon, Snake, and Columbia Rivers to the Pacific. They landed at the mouth of the Columbia River, Astoria, Oregon. The expedition then ended on September 23, 1806 upon their return to St. Louis from Oregon.

If you believe that the expedition began in Pittsburgh, then it took 2 years and 25 days.

If you believe that the expedition began when Clark joined then it took 1 year 11 months and 11 days.