Chicago and Hartford are about 769 miles apart by road. Split the difference and you arrive near Cleveland, the city closest to the halfway point between them. That puts roughly 6 hr 27 min of driving on the Chicago side and 9 hr 46 min on the Hartford side — the fairest single meeting point among the cities near the middle.
That's a half-day drive from each side, so Cleveland suits an overnight or a weekend rather than a quick coffee — long enough to want a reason to stay, short enough to drive.
If Cleveland doesn't have what you're after, Pittsburgh and Buffalo are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Chicago and Hartford.
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.