Sussex County, the southernmost county in Delaware, is bordered on the north by Kent County, on the east by the Atlantic Ocean, and on the west and south by Maryland's Caroline, Dorchester, Wicomico, and Worcester Counties. The boundary between Delaware and Maryland was long disputed. Until the 1760s and the Mason-Dixon survey, Maryland's claim extended well into what is now Sussex County. The border was undefined, but there were Somerset land claims roughly up to the Indian River, and some beyond that. If you've got lines in Sussex County, especially in the southern part, you would be wise to check Maryland records, too.