sentences:  Both were transferred, along with the state's five other western counties (the former Washington District), to Federal jurisdiction in 1790 and formed into the Southwest Territory.The county was divided into Montgomery and Robertson counties in 1796, when Tennessee became the nation's 16th state.The land area formerly included in Tennessee County now forms Humphreys, Montgomery, and Robertson counties and portions of Stewart, Dickson, Cheatham, and Houston counties.