Henan Oirat is a strongly endangered dialect of the Mongolian language spoken by merely a handful of individuals in Henan Mongol Autonomous County (MAC), the southernmost of Huangnan Tibetan Autonomous Prefecture’s (TAP) four counties. Over 90 % of Henan’s population is registered as belonging to the Mongol ethnic group, but the most broadly employed language in the county is Amdo Tibetan. The predecessors of the Henan Oirats were a part of Güüshi Khan’s Oirat Mongols, commonly referred to as Deed Mongols, who came to Qinghai in the seventeenth century. The exploration of the history and language of the Henan Oirats is inseverable from the history and language of the numerous groups of Mongols who had lived in the region prior to Güüshi’s Oirats.