The 31st U.S. State: California, Not Idaho

Correction: The 31st state admitted to the Union was California, on September 9, 1850.

Idaho was the 43rd state, admitted on July 3, 1890.

The original answer confused the order. Here are the 30th–32nd states for context:

• 30th: Wisconsin (May 29, 1848)
• 31st: California (Sep 9, 1850)
• 32nd: Minnesota (May 11, 1858)