The fair place to meet is Indianapolis, IN — the city closest to the midpoint of Chicago and Cincinnati. From the farther side that’s about 3 hr 27 min of driving.
Recommended midpoint
Indianapolis, IN
From Chicago
3 hr 27 min
165 mi to Indianapolis
From Cincinnati
2 hr 29 min
99 mi to Indianapolis
Cincinnati has the shorter trip; the split is off by about 58 min. The alternatives below can even it out. Chicago and Cincinnati are about 252 miles apart.
Chicago and Cincinnati are about 252 miles apart by road. Split the difference and you arrive near Indianapolis, the city closest to the halfway point between them. That puts roughly 3 hr 27 min of driving on the Chicago side and 2 hr 29 min on the Cincinnati side — the fairest single meeting point among the cities near the middle.
At this range, Indianapolis works for a same-day meetup: close enough from both Chicago and Cincinnati to meet for lunch or an afternoon and still be home by evening.
If Indianapolis doesn't have what you're after, Louisville and Columbus are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Chicago and Cincinnati.
Indianapolis, colloquially known as Indy, is the capital and most populous city of the U.S. state of Indiana and the county seat of Marion County. Indianapolis is situated in the state's central till plain region along the west fork of the White River. Read more →
Chicago is the most populous city in the U.S. state of Illinois and in the Midwestern United States. Located on the western shore of Lake Michigan, it is the third-most populous city in the United States, with a population of 2.74 million at the 2020 census. Read more →
Cincinnati is the most populous city in Hamilton County, Ohio, United States, and its county seat. Read more →
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.
Estimates use straight-line distance and typical road speeds; real drive times vary with route and traffic.