A small L-shaped dwelling with a full-length front porch stood on this lot by 1875 according to an early bird's-eye map of Helena. German Catholic rancher Herman Rosenbaum and his wife Mary purchased the house in 1879. The neighborhood was perfect for the Rosenbaums. Two Catholic schools, a convent, a Catholic hospital, and Helena's first cathedral later replaced by St. Helena's made for a thriving Catholic presence just north and west of Rodney Street. The proximity of St. Vincent's Academy for Girls—Montana's first boarding school, which stood where the St. John's building is now— likely appealed to the Rosenbaums, whose daughters attended the academy. Herman arrived in the Helena valley in the 1860s, where he found success supplying beef and farm products to Montana's booming mining towns. Like many successful ranchers, the Rosenbaums lived in town part of the year, allowing their children to attend school. Herman died in 1889, but the family remained in residence until 1903. The family built a rear addition before 1890 and others further expanded the original L-shaped structure.