[1] Mullen came to the United States at the age of nine and left school at fourteen to work in a mill, an occupation that he continued throughout the east, Kansas, and Colorado.
Mullen was born on June 11, 1847[1] in Ballinasloe, County Galway, Ireland[2] during the Great Famine.
[1] The Mullens settled at Oriskany Falls, Oneida County, New York,[2] where Denis and Thomas purchased houses adjacent to each other, and close to the town mill.
[3] John Mullen dropped out of school and worked at age fourteen at the Oriskany Flour Mill.
He settled in Troy, Kansas, where he was in charge of the Banner Flour Mills, owned by Tracey and Parker Company.
[1][2] Over time, Mullen entered the financial sector, first as president of Union Savings and Loan Association, later a director at the First National Bank of Denver.
[11] On October 12, 1874, Mullen married Catherine Smith with whom they had four girls,[1] Katherine, May, Ella, and Edith.
[2] Mullen and Catherine founded a school for orphaned boys that was run and taught by the Christian Brothers of St. John Baptist de La Salle in Santa Fe, New Mexico.