Municipality of Deventer, the Netherlands. Deventer is a municipality and city in the Salland region of the Dutch province of Overijssel. Deventer is largely situated on the east bank of the river IJssel, but also has a small part of its territory on the west bank. In 2005 the municipality of Bathmen (pop. 5,000) was merged with Deventer as part of a national effort to reduce bureaucracy in the country.