His political writing attracted attention by Illinois politicians, and Whitlock was offered a job as Gov. John Peter Altgeld's personal secretary; instead he took a position with the Secretary of State. While in Springfield, he also studied the law under Senator J. M. Palmer; he was admitted to the bar in 1894, at the age of 25.
Whitlock became very active in Illinois Democratic Party politics. In 1894, he was Chair of the Democratic Finance Committee and in charge of arrangements for the state convention.