Like Lincoln, Oglesby was born in Kentucky and spent most of his youth in central Illinois, apprenticing as a lawyer in Springfield and standing for election to the Illinois legislature Congress, and U.S. Senate. Oglesby participated in the battles of Cerro Gordo and Vera Cruz during the Mexican-American War and made a small fortune in the gold rush of 1849. A superlative speaker, he ran unsuccessfully for Congress in a campaign that featured the Lincoln-Douglas debates of 1858, then was elected to the Illinois senate as Lincoln was being elected president.