Hartleton is a borough in Union County, Pennsylvania, United States. The population was 247 at the 2020 census. The borough, as well as the adjoining township of Hartley, are both named for Colonel Thomas Hartley, American politician and Revolutionary War leader, and local landowner. An alternative name was Hartleyton and later shortened to the present name. The original name was Kester's, and named for Peter Kester who was the first tenant of Hartley.