While cities in Island and Snohomish counties established their own libraries in the early 20th century, the first inter-city system was created by voters in unincorporated Snohomish County in 1944. The system's creation was spurred by the state legislature's approval of rural library districts in 1941. The new Snohomish County Library was temporarily headquartered in the basement of the separate
Everett Public Library before moving to another building in Everett. The system's first library was in
Alderwood Manor; the first
bookmobile was purchased in 1947. The state government sponsored demonstration library and
bookmobile projects on Camano and Whidbey islands in 1961, which created interest in establishing an Island County system. The Island County Rural Library District was established by voters in November 1962 and merged with the Snohomish County system on December 17, forming the Snohomish-Island Inter-County Rural Library District. The
board of trustees for the new library system was formed during a meeting on January 11, 1963; after the board members were appointed, they decided to name the system the Sno-Isle Regional Library. A new headquarters building near Marysville was constructed in 1965. Rural branches would rely on property taxes generated within the district, as well as donations from organizations and members of the community. The library system purchased and installed its first computerized catalog system in 1983. Incorporated cities began voting to annex themselves into the Sno-Isle district in the late 1980s, with promises of new libraries and potential cost savings over the contracted service. A major levy lift of 9 cents per $1,000 in assessed property value was approved by voters in May 2018 by a margin of less than 0.5 percent. All Sno-Isle branches were closed in March 2020 due to the
COVID-19 pandemic, but reopened with curbside pick-up service three months later. In-person services resumed at some branches in early 2021. In 2024, the city government of Everett proposed a consolidation of their
city libraries with Sno-Isle to address a budget deficit. The Everett Public Library's board of trustees opposed the proposal, which would require voter approval. ==Branches==