The Unalachtigo were a division of the Lenape (Delaware Indians), a Native American tribe whose homeland Lenapehoking[a] was in what is today the Northeastern United States.

[4] Unalachtigo words were recorded in 17th-century vocabulary drawn from the Sankhikan band of Lenape in New Jersey.

[3] Linguist Ives Goddard has determined that the Unalachtigo had their origins around the Lehigh Valley of Pennsylvania, and adjacent portions of New Jersey.

The group unsuccessfully filed for federal recognition with the Bureau of Indian Affairs on 1 Feb 2002.

[8] In 2005, the Unalachtigo Band of the Nanticoke Lenni Lenape Nation and their tribal chairman James Brent Thomas Sr. sued the State of New Jersey and Governor Donald DiFrancesco for restoration of the Brotherton Reservation lands and the expulsion of non-Indian peoples.