Based 167 km southeast from Saskatoon, the RM of Sarnia No. 221 hosts a population of 322 with a population density of 0.4/km². Within the RM lies the villages of Chamberlain, Dilke, and Holdfast, the resort villages of Alice Beach, Grandview Beach, and Wee Too Beach, and the hamlet of Sarnia Beach. The RM also has the Last Mountain Lake and Arm River within its boundaries. Attractions in the area include the Arm River Recreation Site.