Unlike the other dioceses of the Evangelical Lutheran Church of Finland, the diocese is not formed on a geographical basis. All the Swedish-speaking parishes and dominantly Swedish-speaking bilingual parishes of the church belong to the diocese, regardless of their location.
In addition, there are two ethnicity-based parishes in the diocese: The German parish of Finland and rikssvenska Olaus Petri församlingen, the former Church of Sweden parish in Finland. The German parish () is the parish for the German-speaking minority of Finland, while the rikssvenska parish consists of Swedish citizens living in Finland.