Grant County is a county in central Indiana in the United States Midwest. At the time of the 2020 census, the population was 66,674. The county seat is Marion. Important paleontological discoveries, dating from the Pliocene epoch, have been made at the Pipe Creek Sinkhole in Grant County.

Marion is a city in and the county seat of Grant County, Indiana, United States, along the Mississinewa River. The population was 28,310 as of the 2020 census. It is named for Francis Marion, a brigadier general from South Carolina in the American Revolutionary War.