Alonsa is a rural municipality (RM) in the province of Manitoba, western Canada. It lies on the west side of Lake Manitoba.

Located within the borders of the municipality is the Indian reserve of Ebb and Flow 52, as well as the 60,000 m (6 ha) Margaret Bruce Beach Provincial Park, located 12 km (7.5 mi) east of the town of Alonsa, on one of a series of sand ridges that extend the length of the west side lake. The park is currently under lease to a private operator but development plans include a provincial campground and day use facility.

The incorporation of Alonsa on 1 January 1945 was as a Local Government District (LGD). It received rural municipality status on 1 January 1997.

Communities

Demographics

In the 2021 Census of Population conducted by Statistics Canada, Alonsa had a population of 1,210 living in 492 of its 659 total private dwellings, a change of -3% from its 2016 population of 1,247. With a land area of 3,006.17 km (1,160.69 sq mi), it had a population density of 0.4/km (1.0/sq mi) in 2021.