Longtime allies of the Cheyenne, the Arapaho (who historically referred to themselves as Inuna-Ina), are an Algonquian-speaking people, based mostly in the Great Plains.
Today, there are two main Arapaho tribes: the Northern Arapaho, who number about 6000 and are concentrated in Wyoming, and the Southern Arapaho, who are united with the Cheyenne into the Cheyenne-Arapaho Nation in Oklahoma, with a combined 11,000 members.
Text adapted from native-languages.org