Smithsonian trinomials are unique identifiers assigned to archaeological sites in many states in the United States. They are composed of one or two digits coding for the state, typically two letters coding for the county or county-equivalent within the state, and one or more sequential digits representing the order in which the site was listed in that county. The Smithsonian Institution developed the site number system in the 1930s and 1940s. (Trinomials are now assigned by the individual states.) The 48 states then in the union were assigned numbers in alphabetical order. Alaska was assigned number 49 and Hawaii was assigned number 50 after those states were admitted to the union. There are no Smithsonian trinomial numbers assigned for the District of Columbia or any United States territories.