The town of Oglesby, Illinois, is named in his honor,[1] as is an elementary school situated in the Auburn Gresham neighborhood of Chicago's south side.

[5] With the outbreak of the Mexican–American War, he enlisted as a 1st Lieutenant in Company C, 4th Illinois Volunteer Infantry Regiment [6] taking part in the battles of Veracruz and Cerro Gordo "where his regiment almost captured Mexican President General Santa Anna, but they had to settle for his cork leg, carriage and $20,000 in gold".

[7] He might have participated in what may have been the first baseball game ever played outside the U.S., at the end of April 1847, a few days after the Battle of Cerro Gordo, "with the wooden leg captured (by the Fourth Illinois regiment) from General Santa Anna".

Oglesby sustained severe injuries in the Battle of Corinth in 1862 and was elevated to the status of major general that same year.

However, at the request of Abraham Lincoln, he abandoned his commission in 1864, successfully running for Illinois governor on the Republican ticket.

During his tenure as governor, he advocated improving the quality of care of the mentally ill and for other groups of disabled citizens.