400 (2016 population: 598) is a rural municipality (RM) in the Canadian province of Saskatchewan within Census Division No.

In the 2021 Census of Population conducted by Statistics Canada, 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.

[3] The reeve of the RM is Allen Baumann while its administrator is Tim Schmidt.

[3] The RM's office is located in Middle Lake.