The Rural Municipality of Grass Lake No. 381 (2016 population: ) is a rural municipality (RM) in the Canadian province of Saskatchewan within Census Division No. 13 and Division No. 6.
The RM of Grass Lake No. 381 incorporated as a rural municipality on December 13, 1909.
The following unincorporated communities are within the RM.
In the 2021 Census of Population conducted by Statistics Canada, the RM of Grass Lake No. 381 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 Grass Lake No. 381 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 Grass Lake No. 381 is governed by an elected municipal council and an appointed administrator that meets on the first Tuesday of every month. The reeve of the RM is Scott Vetter while its administrator is Theresa Poschenrieder. The RM's office is located in Luseland.