Because his identity was obscured until his death in 1904, the circumstances of his birth are unclear, and census records suggest he may have been born as Mary Manumon, though the family also had a young servant girl, Johanna Burke.

Accounts to journalists after his death claimed that Monahan's mother dressed the young child in boy's clothing in early childhood to sell newspapers on the street.

[2]: 99 Monahan had spent his early years in Idaho as a cowboy, and briefly lived in Oregon before returning to Owyhee County, where an 1898 directory listed him as a cattle rancher.

[2]: 97 Monahan lived on Succor Creek, near Silver City, in a small home with dirt floors, raising pigs and chickens.

In a letter to the Buffalo police chief seeking next of kin, a local resident remarked that, "He had fought his way through with many of us ... suffered hardship and hunger in early days and never whimpered ... the cowboys treated him with the greatest respect, and he was always welcome to eat and sleep at their camps.