My supposition in yesterday's posting was true! Betsy-Tacy fans have helped confirm the "Tower House" in Mankato was indeed the home of James Hickey! 

The 1904 Mankato City Directory shows the Hickeys living at 127 Bradley Street, located at the corner of Center and Bradley. A more recent photo of the house is shown at right. James Hickey had several positions but at one time managed a plant which manufactured agricultural equipment (e.g., threshing machines). In any case, he prospered financially as evidenced by  the construction of this magnificent home.

Maud Hart Lovelace lived nearby as a young girl and apparently admired the house's tower feature. When she wrote the Betsy-Tacy series, she "borrowed" the tower from the Hickey house for her friend Tib's home.