At Woodport, Lake Hopatcong ends as Route 181 crosses the line from Morris County to Sussex County. Now in the town of Sparta, Route 181 becomes Woodport Road, winding northward back toward Route 15. The two routes parallel northwestward and intersect with Blue Heron Drive, which connects the two roads. Once again, Route 181 turns northwest and away from Route 15, reaching downtown Sparta. The two-lane road winds northwest through the center of Sparta, reaching a junction with County Route 517 (CR 517; Sparta Avenue), which connects to Route 15 once again.