The Defence Corps building was commissioned by the Southern Ostrobothnia Defence Corps, which used the three-storey building with mixed functions as its headquarters. The main building was originally used as offices for the Civil Guard of South Ostrobothnia and the Lotta Svärd Association. The top tier of the building was in residential use.
The semi-subterranean ground floor, which contains a circular assembly hall, foyer and cloakroom, is built of stone; the office level and the residential storey (at the top with its own access stairs) are of wood. Together with the main building, a separate outbuilding was designed and erected on the other side of the courtyard. The ground floor of this two-storey building of rendered brick contains a garage, guardhouse, arms depot, sauna, and laundry; there are four small apartments in the upper storey. An unusual stair arrangement on both sides of the arched entrance provides separate access to most of the various facilities. One of the short sides of the courtyard is enclosed by a low wooden storehouse, designed some years later. The courtyard itself was intended as a drill and parade ground.
After the Second World War the building was re purposed for other uses. Since then many tenants have been operating in the building, including The Federation of Finnish youth association, a school and a travel agency. Nowadays the building is managed by the Provincial Museum of Southern Ostrobothnia. Currently it houses the Civil Guard and Lotta Svärd Museum. The main building holds museum exhibition and meeting spaces, an info booth and museum shop. The outbuilding has more exhibition spaces and a administration space for the museum.
The Defence Corps building has been preserved in its original condition and it’s buildings and their yard have also been protected under the law regarding building protection since 2002.
The building represents refined neoclassicism and functionalist features as well as Ostrobothnian construction heritage. The building’s unusual stair hall, facade pilasters, and assembly hall painted in Pompeiian style make it one of the chief works of Alvar Aalto’s Neo-Classical period. Some part of the decorations in the buildings, including furniture, lamps and ornament details were also designed by Aalto.
Aalto originally designed a loggia-like staircase for the end entrance, but it was not built.
The Suojeluskuntalainen statue, work by artist Pentti Papinaho is located in the yard of The Defence Corps building.