Simplify the following text for a Grade 6 native English-speaking person.
Original: Saint-Denis-d ` Anjou is a commune in the Mayenne department in north-western France .
Simplified: Saint-Denis-d ` Anjou is a commune of 1 337 people ( 1999 ) . It is found in the region Pays de la Loire in the Mayenne department in the northwest of France .