In a research project, the Mannheim University Library digitized several German directories of municipalities (Gemeindeverzeichnisse) from the period between 1880 and 1976. The publication contains historical population censuses and population surveys at municipal level from the German Reich, the Federal Republic of Germany and the German Democratic Republic. A full text search is available by processing the scans with OCR software.
The digitized resources of the RDC can be accessed without asking for permission. Further information can be found here: Public Domain Mark 1.0.