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Events on Thursday 3 December 1818 1
1818Illinois admitted as a U.S. stateIllinois becomes the 21st state of the UnionIllinois was admitted to the United States as the 21st state, having met the population threshold required under the Northwest Ordinance. Kaskaskia served as its first capital. The new state's borders extended further north than originally planned to secure access to Lake Michigan.