Del. Code tit. 9, § 104

Sussex County comprises that part of the State which is bounded as follows: On the north, by the southerly boundary line of Kent County as described in § 103 of this title; on the east, by the middle line of Delaware Bay from the point where the same is intersected by southerly boundary line of Kent County to the mouth of the Bay, and by the Atlantic Ocean; on the south and west by the State of Maryland.