In February 1846 , Wilmington was founded as a township by combining parts of Neshannock Township in Lawrence County with parts of the Lackawannock Township at Mercer County . Wilmington was established as a township in February 1846 by combining parts of Neshannock Township in Lawrence County with parts of Lackawannock Township in Mercer County . In February 1846 , Wilmington was founded as a township by combining parts of Neshannock Township at Mercer County with parts of the Lackawannock Township in Lawrence County .