I'm looking for free state border layers for Germany. Are there any free sources for such data?
You can download free state border layers of Germany from DIVA-GIS by selecting
Administrative areas as the subject.
At http://www.geodatenzentrum.de/ you will find boundarys from the local community up to the national border.
Natural Earth is a great source for reference boundary data
You can also check this website for Germany data,
It is free openstreetmap data.
You can download state borders for Germany from the GADM data source
1. level-0 | Country
2. level-1 | State
3. level-2 | District
4. level-3 | Municipality
5. level-4 | Town
These data were extracted from the GADM database (https://www.gadm.org), version 3.4, April 2018. They can be used for non-commercial purposes only. It is not allowed to redistribute these data, or use them for commercial purposes, without prior consent. See the website (https://www.gadm.org) for more information.