Route 166 is a short, 3.73-mile (6.00 km) state highway in Ocean County, New Jersey. The route provides an alternate alignment of U.S. Route 9 through South Toms River and Toms River. The southern terminus is at an intersection with U.S. Route 9 northbound in Beachwood, where it heads northward along Atlantic City Boulevard. The route continues until ending where U.S. Route 9 leaves the Parkway north of Toms River. US 9 itself uses the Garden State Parkway to bypass Toms River.

U.S. Route 9 (US 9) is a United States Numbered Highway in the Mid-Atlantic region of the United States, running from Laurel, Delaware, to Champlain, New York. In New Jersey, the route runs 166.80 miles (268.44 km) from the Cape May–Lewes Ferry terminal in North Cape May, Cape May County, where the ferry carries US 9 across the Delaware Bay to Lewes, Delaware, north to the George Washington Bridge in Fort Lee, Bergen County, where the route along with Interstate 95 (I-95) and US 1 continue into New York City. US 9 is the longest U.S. Highway in the state.