Princeton Junction is an unincorporated community and census-designated place (CDP)[9] located within West Windsor township, Mercer County, in the U.S. state of New Jersey.

[3] Following the mid-1860s relocation of the Camden & Amboy rail line from next to the Delaware & Raritan Canal to the present location of the Northeast Corridor, and the subsequent construction of a train station south of the intersection of Washington Road and the new rail line, a community called "Princeton Junction" developed.

This community originally featured several farmhouses, a hotel, a general store, a feed mill, and several other businesses centered around the intersection of Station Drive and Washington Road, profiting off of access to other cities provided by the rail line.

[12] Princeton Junction is currently the proposed site of a "transit village" to be built northwest of the train station.

[12] Princeton Junction is in eastern Mercer County, in the northern part of West Windsor Township.

The northeastern boundary of the community is the Millstone River, across which is Plainsboro Township in Middlesex County.

Bear Brook, a tributary of the Millstone, forms the eastern border of Princeton Junction, and the CDP extends north as far as U.S. Route 1.

Princeton Junction's name comes from the train station of the same name, now on the Amtrak and New Jersey Transit Northeast Corridor.

The station is the junction between this main line and a spur served by the "Dinky" train, run by New Jersey Transit, to Princeton itself.

[16] Some residents blame the "deterioration" of the central Princeton Junction area on a lack of political consensus.