Lebanon is a city in and the county seat of Laclede County in Missouri. The population was estimated at 15,013 at the time of the 2020 cens…Lebanon is a city in and the county seat of Laclede County in Missouri. The population was estimated at 15,013 at the time of the 2020 census. It is the county seat of Laclede County. The Lebanon Micropolitan Statistical Area consists of Laclede County.