39th meridian west from Washington

The 39th meridian west from Washington is an archaic meridian based on the Washington meridian. The meridian is used as a boundary for two states.

The first and only usage of the meridian as a boundary occurred in 1864. In that year, the Montana Territory was created from Idaho Territory with the meridian serving as its extreme northwestern boundary. Montana became a state in 1889, with Idaho following the next year.