Mayenne is a commune in the Mayenne department, northwestern France. It is a subprefecture of the department. It is situated on the river May…Mayenne is a commune in the Mayenne department, northwestern France. It is a subprefecture of the department. It is situated on the river Mayenne. In medieval times, the town was the seat of the Lords of Mayenne. The town originated when Juhel II of Mayenne built a monastery near the gate of the pre-existing castle, which led to the formation of the settlement.