The Osage Indian murders were a series of murders of Osage in Osage County, Oklahoma, during the 1910s–1930s. Newspapers described the increasing number of unsolved murders and deaths among young adults as the "Reign of Terror". Most took place from 1921 to 1926. Some sixty or more wealthy, full-blood Osage persons were reported killed from 1918 to 1931. Newer investigations indicate that other suspicious deaths during this time could have been misreported or covered-up murders, including those of individuals who were heirs to future fortunes. Further research has shown that the death toll may have been in the hundreds.

The Osage Nation is a Midwestern American tribe of the Great Plains. The tribe developed in the Ohio and Mississippi river valleys around 700 B.C. along with other groups of its language family. They migrated west after the 17th century, settling near the confluence of the Missouri and Mississippi rivers, as a result of Iroquois expansion into the Ohio Country in the aftermath of the Beaver Wars.