The fair place to meet is Chicago, IL — the city closest to the midpoint of Indianapolis and Milwaukee. From the farther side that’s about 3 hr 27 min of driving.
Recommended midpoint
Chicago, IL
From Indianapolis
3 hr 27 min
165 mi to Chicago
From Milwaukee
2 hr 2 min
81 mi to Chicago
Milwaukee has the shorter trip; the split is off by about 1 hr 25 min. The alternatives below can even it out. Indianapolis and Milwaukee are about 243 miles apart.
Indianapolis and Milwaukee are about 243 miles apart by road. Split the difference and you arrive near Chicago, the city closest to the halfway point between them. That puts roughly 3 hr 27 min of driving on the Indianapolis side and 2 hr 2 min on the Milwaukee side — the fairest single meeting point among the cities near the middle.
At this range, Chicago works for a same-day meetup: close enough from both Indianapolis and Milwaukee to meet for lunch or an afternoon and still be home by evening.
If Chicago doesn't have what you're after, Cincinnati and Detroit are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Indianapolis and Milwaukee.
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 →
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 →
Milwaukee is the most populous city in the U.S. state of Wisconsin. It is located on the western shore of Lake Michigan at the confluence of the Milwaukee, Menomonee, and Kinnickinnic Rivers. 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.