The 20th century brought many changes to Mission Hill. The Sanborn Fire Insurance Map of 1974 [19] shows that the entirety of Whitney Street and the accompanying row houses from Worthington to St. Alphonsus Streets were replaced by two large apartment buildings. Back Bay Towers, built in 1965, housed 146 units. Directly behind this building was a garage and another apartment complex housing 270 units and a garage with a capacity of 300 cars. These buildings demonstrate a significant increase in the demand for housing in the city and the limited amount of space forced new construction upwards. The owners of the earlier single family homes would have been forced to relocate to another part of the city or to the completed apartment complexes. Another factor contributing to the lack of space for housing was the leveling of parts of blocks for parking lots as the presence of a gas filling station in Mission Hill reinforces the increased dependability on the automobile.

The increased amount of housing units in Mission Hill also made it necessary to expand the educational facilities in the neighborhood. Additions to the Primary School, now named the Maurice J. Tobin School after a former mayor and governor from Boston, included a new wing, a gym and a hall. Also to serve the increased population, the Mission Hill Municipal Building replaced the flats and single family homes from Sherbrooke to Faxon Street, and the Parker Hill Branch of the Boston Public Library moved from its rented storefront to and enlarged building by the park.