The Rural Municipality of Three Lakes No. 400 (2016 population: ) is a rural municipality (RM) in the Canadian province of Saskatchewan within Census Division No. 15 and Division No. 5.
The RM of Three Lakes No. 400 incorporated as a rural municipality on January 1, 1913.
The following urban municipalities are surrounded by the RM.
The following urban communities are within the RM.
In the 2021 Census of Population conducted by Statistics Canada, the RM of Three Lakes No. 400 had a population of living in of its total private dwellings, a change of from its 2016 population of . With a land area of , it had a population density of in 2021.
In the 2016 Census of Population, the RM of Three Lakes No. 400 recorded a population of living in of its total private dwellings, a change from its 2011 population of . With a land area of , it had a population density of in 2016.
The RM of Three Lakes No. 400 is governed by an elected municipal council and an appointed administrator that meets on the second Wednesday of every month. The reeve of the RM is Allen Baumann while its administrator is Tim Schmidt. The RM's office is located in Middle Lake.