The Idaho Northern Railroad built a branch line of the Oregon Railroad and Navigation Company (OR&N) in northern Idaho, U.S., connecting the main line at Enaville with Paragon, a distance of 32.83 miles (52.83 km). The company was incorporated on January 10, 1906, and opened on August 1, 1909 as an operating subsidiary of the Union Pacific Railroad (UP), owner of the OR&N. On December 23, 1910, the property of the OR&N and Idaho Northern Railroad were conveyed to new UP subsidiary Oregon–Washington Railroad and Navigation Company.
The line was cut back from Paragon to Prichard after a December 1917 washout. A flood in December 1933 severely damaged the remainder of the line, and the Interstate Commerce Commission authorized its abandonment in 1935.