In 1860, he was elected clerk of the circuit court, then co-founded a Union League of America chapter, later serving at the state level of the organization.
Harlow was the personal secretary to Governor Richard J. Oglesby and oversaw Camp Butler starting in 1864.
Harlow studied architecture under Otis L. Wheelock, who worked at the time in Watertown, New York.
In March 1854, Harlow moved to Pekin, Illinois, to establish a carpentry and architecture shop.
[2] Oglesby commissioned Harlow an Illinois colonel and tasked him with the oversight of Camp Butler in Springfield.
[4] Harlow ran for Illinois Secretary of State in 1868, but the Republican Party instead decided to put Edward Rummel on the ticket.