Decatur County is located in southeast Indiana at the intersections of Interstate 74 and State Road 3. The County Seat of Decatur County is Greensburg. Greensburg, Indiana, occupies a unique place among the cities of the world by reason of trees that are growing from the roof of its courthouse tower. The population of Decatur County is approximately 25,000, with 11,000 of those people living in Greensburg.