1921 Missouri half dollars mark the 100th anniversary of the Show-Me State's admission to the Union as the 24th state. The coins, designed by Robert Aitken, were issued in two different varieties: one with a numerical inscription 2*4 indicating Missouri's place as the 24th state and another without the marking; these are known as plain Missouri half dollars.

While it is unknown exactly how many 1921 Missouri 2*4 halves were distributed, but they are one of the rarest regular issues in the classic commemorative series. Most of the Missouri 2*4 half dollars are found in AU50 to MS64 grades, with MS65 rare and pieces grading MS66 or higher proving very rare.