It is named for John McLean, a senator. The seat and largest city are both Bloomington.
It borders Woodford, Livington, Ford, Champain, Piatt, DeWitt, Logan and Tazewell Counties.
Main Highways include I-39, I-55, I-74, US-24, US-51, US-136, US-150, IL-9, IL-54 and IL-251. In addition, historic route 66 ran through the county.