Sipoo is a municipality of Finland. It is part of the Helsinki metropolitan area. The municipality has a population of 22,595 (31 December 2023) and covers an area of 698.60 square kilometres (269.73 sq mi) of which 358.97 km2 (138.60 sq mi) is water. The population density is 66.52 inhabitants per square kilometre (172.3/sq mi). The administrative center of the municipality is Nikkilä, which is located 34 kilometres (21 mi) northeast of the center of Helsinki. Another significant urban area is Söderkulla, located in the southern part of the municipality.

The municipalities represent the local level of administration in Finland and act as the fundamental, self-governing administrative units of the country. The entire country is incorporated into municipalities and legally, all municipalities are equal, although certain municipalities are called cities or towns. Municipalities have the right to levy a flat percentual income tax, which is between 16 and 22 percent, and they provide two thirds of public services. Municipalities control many community services, such as schools, health care and the water supply, and local streets. They do not maintain highways, set laws or keep police forces, which are responsibilities of the central government.