The Subnational Government Structure and Finance Dashboard displays comparable graphs on the institutional organisation and public finance at the subnational government level for 38 OECD member countries. The graphs show the weighted averages for unitary and federal countries, as well as the average for the European Union and the OECD for the latest year available.
This section includes graphs on municipalities by population class size. You may find the full dataset here: Municipal level government by population size.
The data is also available in PDF format.