Greensburg is a city in Decatur County, Indiana, United States. The population was counted at 11,492 at the 2010 census. The city is the county seat of Decatur County. The Decatur County Courthouse in Greensburg, Indiana, is known for a tree which grows from the top of the Courthouse Tower, giving Greensburg its nickname of the "Tree City. There have been one or more trees growing continually since the first tree was noticed in the early 1870s. Later, other small trees appeared on the clock tower.