Montana has 56 counties. The 1955 passenger plates were in pairs, and they were renewed with a tab for 1956. This plates are of steel composition and usually have "prison made" stamped on the edge.

The order of population and the number of registrations sold in 1932 generally determined the ranking of the county numbers, although there are many outliers. The 1933 system was based on earlier numbers, so the rankings were no longer particularly accurate in 1955 (or today either, for that matter).