Ille-et-Vilaine is a department of France, located in the region of Brittany in the northwest of the country. It is named after its two main rivers, the …Ille-et-Vilaine is a department of France, located in the region of Brittany in the northwest of the country. It is named after its two main rivers, the Ille and the Vilaine. It had a population of 1,079,498 in 2019.