Riddle Hill is a rural unincorporated community located in Curran and Gardner townships, Sangamon County, Illinois.

It is a crossroads located adjacent to where Old Jacksonville Road crosses Little Spring Creek, 6.5 miles west of Springfield.

Starting as early as the 1830s, travelers used the place where this road forded the creek as a campground, and the community grew from there.

The camping place is identified as 'McCoy's Mill', apparently recalling the name of a gristmill on Little Spring Creek at the ford.

A historical marker in the yard of the New Salem Methodist Church commemorates the site of a now-vanished tree that marked the campsite.