Lebanon is a city in Smith County, Kansas, United States, in the north central part of the state. As of the 2010 census, the city population was 218.In 1918, a scientific survey established the geographic center of the 48 contiguous U.S. states about 2.6 miles northwest of Lebanon, and a monument was subsequently erected at the site. The geographic center of the 50 U.S. states is located near Belle Fourche, South Dakota.