The Johnson County Museum of History occupies one of the historic buildings near the courthouse square and covers the county's development from pre-settlement Indigenous occupation through the 20th century. Exhibits touch on the county's role in Indiana agriculture, the railroad era that made Franklin a market hub, and local figures who shaped the region.
It's a modest local history museum rather than a major destination, but if you're already on the square it fills an hour well. The staff tends to be local and knowledgeable about county history beyond what the exhibits show.