New Jersey State Route 31 is a north-south highway in Northwestern Mercer County. it runs from U.S. Rt. 206/BUSN U.S. Rt. 1, at Trenton to the Mercer/Hunterdon County Line, near Woodsville. NJ St Rt 31 passes through the following towns in Mercer County. Trenton Ewing Marshalls Corner NJ St Rt 33 is not multi-plexed in Mercer County. NJ St Rt 33 intersects the following highways in Mercer County. U.S. Rt. 206, at Trenton. BUSN U.S. Rt. 1, at Trenton. Interstate 295, near Trenton.