is a county in Norway, bordering Buskerud and Telemark. The county administration is in Tønsberg, and the largest city is Sandefjord. With the exception of Oslo county, Vestfold is the smallest county in Norway by area.
Vestfold is located west of the Oslofjord, as the name indicates. It includes many smaller, but well-known towns in Norway, such as Larvik, Sandefjord, Tønsberg and Horten. The river Numedalslågen runs through the district. Many islands are located at the coast. Vestfold is mostly dominated by lowland and is among the best agricultural areas of Norway. Winters last about three months, while pleasant summer temperatures last from May to September, with a July average high of 17°C (63°F) (Tønsberg climate).
Vestfold is traditionally known for shipping and sailing. Sandefjord was formerly a headquarters for the Norwegian whaling fleet, and Horten used to be an important naval port. The coastal towns of Vestfold now engage in fishing and shipbuilding. Some lumbering is carried on in the interior. The district also includes some of the best farmland in Norway. Vestfold is the only county in which all municipalities have declared Bokmål to be their sole official written form of the Norwegian language.
Kaupang, a town from the Viking Age is believed to be the first town in Norway, although Tønsberg is the oldest town in Norway still existing. Kaupang is mentioned under the name of (Kaupangen i Skiringssal) in Ohthere from Hålogaland's tales which date from the 9th century.
By the 10th century the local kings had established themselves as the first dynasty to begin the unification of Norway. The king or his ombudsman resided in the old Royal Court at Sæheimr, today the (Jarlsberg Hovedgård) in Tønsberg. The farm became the seat for Haugathing, the Thing for Vestfold and one of Norway's most important place for the proclamation of kings.