Sidney is a city in Shelby County, Ohio, United States. The population was 21,229 at the 2010 census. It is named after English poet Sir Phillip Sidney and is the county seat of Shelby County. As well, many of the city's elementary schools are also named after famous writers, such as Emerson, Longfellow and Whittier. Sidney was the recipient of the 1964 All-America City Award. In 2009, it was the subject of the documentary film 45365.