Grand Prairie is a city in the United States in Dallas County, Tarrant County, and Ellis County, Texas. It is part of the Dallas ? Fort Worth metroplex Mid-Cities area. It has a population of 175,396 making it the state's fifteenth-most populous city. The city has a total area of 81.1 square miles, 72.1 square miles of which is land and 9.0 square miles or 11.08 percent is water, according to the U.S. Census Bureau. Grand Prairie has a long tradition of Johnson Creek Flooding. A major project of the Army Corps of Engineers was initiated in the 1980s to straighten the river, which has reduced flood damage.