Mosterøy is an island and former municipality

Municipality

A municipality is essentially an urban administrative division having corporate status and usually powers of self-government. It can also be used to mean the governing body of a municipality. A municipality is a general-purpose administrative subdivision, as opposed to a special-purpose district...

 in Rogaland

Rogaland

is a county in Western Norway, bordering Hordaland, Telemark, Aust-Agder and Vest-Agder. It is the center of the Norwegian petroleum industry, and as a result of this, Rogaland has the lowest unemployment rate of any county in Norway, 1.1%...

 county, Norway. The administrative centre was Askje.

It was created by a split from Rennesøy

Rennesøy

Rennesøy is a municipality in Rogaland county, Norway. It is part of the region of Ryfylke. The administrative center is the village of Vikevåg....

 municipality on 1 July 1884. The new municipality had a population of 1,309. On 1 January 1923 a group of outlying islands were separated from Mosterøy to form a separate municipality Kvitsøy

Kvitsøy

Kvitsøy is a municipality in Rogaland county, Norway. It is the smallest municipality in Norway . Kvitsøy was separated from Mosterøy on 1 January 1923.The municipality is an archipelago situated northwest of the coast of the Stavanger peninsula...

. The split left Mosterøy with 745 inhabitants.

On 1 January 1965 Mosterøy was reunited with Rennesøy. Prior to the merger Mosterøy had a population of 817.

On Mosterøy is located Utstein Abbey, the best-preserved medieval monastery in Norway.