Roussillon (French pronunciation: [ʁusijɔ̃] ⓘ) is a regional county municipality in the Montérégie region of Quebec, Canada.

The seat is in Saint-Constant, Quebec.

The region's population was 171,443 as of the 2016 census.

[3] There are 11 subdivisions and one native reserve within the RCM:[2]

Highways and numbered routes that run through the municipality, including external routes that start or finish at the county border:[9]