Fergus County was named for James Fergus. Originally from Scotland, Fergus left home at the age of 20 and started his life in North American. He became a pioneer and he joined the Fisk Expedition to Idaho Territory. He lived and mined in Bannack, Virginia City and eventually Last Chance Gulch. In 1880 he and his son began moving the family ranch to Armells Creek north of the Judith Mountains. In 1883 Fergus provided the finances to move his brother William Fergus and his family of 10 to Montana where they both ranched.

William Fergus's daughter Christina married David Hilger and became the postmistress of a post office that would eventually become named Christina in her honor. Today, Christina is still home to a handful of families. A red barn with the words “Christina, Montana” marks its existence.