Landen is a census-designated place in Deerfield Township, Warren County, Ohio, United States. The population was 6,995 at the 2020 census. It is located around Columbia Road and Montgomery Road in the southeastern part of the township. It surrounds Twenty Mile Stand and near Fosters. Landen was named after Theodophilus James Landen, an early Ohio settler who owned the farmland surrounding Twenty Mile Stand. The man-made Landen Lake occupies the center of the residential area in the town.