The carriage house belonged to the Watson family and housed transportation vehicles from carriages to cars throughout its service. When the Historical Society owned the property, it also included the Erie Planetarium, a popular attraction inside. The Historical Society transferred the planetarium to Penn State Behrend where it is now called the Yahn Planetarium.
The carriage house includes the gift shop, research area, reading room and library with more than 5,800 books published in the 19th, 20th and 21st centuries. The Hagen History Center staff offices are also in the building.