Ruhnu Parish is a municipality in Saare County, Estonia. It encompasses the island of Ruhnu in the Gulf of Riga, together with a number of uninhabited islets. Its population is the smallest of any of Estonia's 79 municipalities, the parish being exempt from the usual minimum population size of 5000. There are 60 permanent inhabitants during winter time; in summer the number increases to 150. In 2015 the parish council approved Ado Tuuga's designs for the municipality's flag and coat of arms.

Saare County is one of 15 counties of Estonia. It consists of Saaremaa, the largest island of Estonia, and several smaller islands near it, most notably Muhu, Ruhnu, Abruka and Vilsandi. The county borders Lääne County to the east, Hiiu County to the north, and Latvia to the south. In 2022 Saare County had a population of 31,292, which was 2.4% of the population of Estonia.