Herculaneum is a city in Jefferson County, Missouri, United States. The population estimate in 2008 was 3,582. It was 2,805 at the 2000 census. The City of Herculaneum was the first county seat of Jefferson County from January 1, 1819 to 1839. The city celebrated its Bicentennial throughout the year in 2008. The City of Herculaneum has received the Tree City USA designation by the Arbor Day Foundation for the past three years - 2007, 2008 and 2009.