An election to Somerset County Council took place on 4 June 2009 as part of the 2009 United Kingdom local elections, having been delayed from 7 May, to coincide with elections to the European Parliament. The result brought to an end 16 years of Liberal Democrat rule to a Conservative controlled administration. 58 councillors were elected from various electoral divisions, which returned one county councillor each. Members were elected by the first-past-the-post voting system for a four-year term of office. This was the last election before the number of seats was cut to 55 for the 2013 election. With a total of 58 seats being reduced to 55 for the next election.
All locally registered electors (British, Irish, Commonwealth and European Union citizens) who were aged 18 or over on Thursday 2 May 2013 were entitled to vote in the local elections. Those who were temporarily away from their ordinary address (for example, away working, on holiday, in student accommodation or in hospital) were also entitled to vote in the local elections, although those who had moved abroad and registered as overseas electors cannot vote in the local elections. It is possible to register to vote at more than one address (such as a university student who had a term-time address and lives at home during holidays) at the discretion of the local Electoral Register Office, but it remains an offence to vote more than once in the same local government election.
The Liberal Democrats lost overall control of the council to the Conservatives who went on to form a majority administration. The Liberal Democrat group became the council's official opposition. Meanwhile the Labour Party had their number of seats halved from 4 to 2. No independents or candidates from other parties were elected as councillors.
The candidates in bold were elected councillors on 4 June 2009.