John O'Fallon (November 17, 1791 – December 17, 1865) was a businessman, philanthropist, and military officer, a nephew of the explorer William Clark.

His father, James O'Fallon, was a physician who served as a surgeon in Washington's army during the Revolutionary War.

[7] In 1817, O'Fallon inherited four enslaved men and women - Patsy, Sousen, Frank and Alley - according to the terms of his grandfather's 1799 will.

However, on July 31, 1818, he resigned his commission, returned to St. Louis, and secured a post as sutler to the Yellowstone Expedition.

When it took two years to even reach Fort Lisa (near present-day Council Bluffs, Iowa), Congress cut its funding.

[15] In 1823, he turned his sutler's business over to a close friend (James Kennerly) and began farming and making whiskey with his half-brother in Louisville, Kentucky.

[16] His whiskey trade apparently didn't hurt his reputation; in 1822 St. Louis elected him Representative to the first Missouri State Legislature, and re-elected him in 1824.

He also financially supported Washington University's medical college[18] and founded O'Fallon Polytechnic Institute.