Grain Valley is a city in Jackson County, Missouri, in the United States. Grain Valley is located in the Kansas City Metropolitan Area and is a suburb of Kansas City, Missouri. It is approx. 23 miles east of Kansas City. The population was 12,854 as of the 2010 census.Grain Valley was founded in the 1870s. It was named for the general character of the grain-producing region.According to the United States Census Bureau, the city has a total area of 6.07 square miles (15.72 km2), of which, 6.06 square miles (15.70 km2) is land and 0.01 square miles (0.03 km2) is water. Nickname- The Valley.