 Prior to 1927, Route 173 was part of Pre-1927 Route 9, which was designated in 1917 to run from Phillipsburg to Elizabeth. In the 1927 New Jersey state highway renumbering, the route became Route 28. In addition, it was also designated as part of U.S. Route 22. In the 1953 New Jersey state highway renumbering, which eliminated long concurrencies between U.S. and State Routes, the Route 28 designation was removed along this portion of the route, leaving U.S. Route 22 the sole number along the route. In the late 1950s, construction began on Interstate 78 through the area. Construction of the portion of Interstate 78 built between Exit 11 (County Route 614) and Exit 13 in Union Township, completed in 1962, modified the alignment of U.S. Route 22 between these two points. It involved the creation of new eastbound lanes for Interstate 78 and conversion of the eastbound lanes of U.S. Route 22 into the westbound lanes of Interstate 78. The westbound lanes of U.S. Route 22 were turned into a two-lane frontage road. In 1969, U.S. Route 22 was moved to the Interstate 78 alignment between Exit 3 in Greenwich Township and Exit 18 in Clinton Township. The former U.S. Route 22 became Route 173 between Exit 3 and Route 31 in Clinton Township, with the remainder of the former U.S. Route 22 alignment becoming county-maintained Beaver Avenue (currently County Route 626).
