Lebanon is a city in Smith County, Kansas, United States. As of the 2020 census, the population of the city was 178. Lebanon was founded in …Lebanon is a city in Smith County, Kansas, United States. As of the 2020 census, the population of the city was 178. Lebanon was founded in 1876 at a site about 4 miles distant from its present site. It was moved to the new site in about 1887–1888. Lebanon is named after Lebanon, Kentucky.