The Rural Municipality of Lake Johnston No. 102 (2021 population: ) is a rural municipality (RM) in the Canadian province of Saskatchewan within Census Division No. 3 and Division No. 2. Located in the southwest portion of the province, it is north of the town of Assiniboia and south of the city of Moose Jaw.
The RM of Lake Johnston No. 102 incorporated as a rural municipality on December 9, 1912.
The following urban municipalities are surrounded by the RM.
The following unincorporated communities are within the RM.
In the 2021 Census of Population conducted by Statistics Canada, the RM of Lake Johnston No. 102 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 Lake Johnston No. 102 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.
Two nearby conservation areas include the Old Wives Lake Bird Sanctuary and the Isle of Bays Wildlife Refuge. They are and north of Expanse respectively.
The RM of Lake Johnston No. 102 is governed by an elected municipal council and an appointed Administrator that meets on the second Tuesday of every month. The reeve of the RM is Sacha Martens while its Administrator is Boyd Holland. The RM's office is located in Mossbank.