Helgö is an island in Ekerö Municipality in , Sweden. Helgö is an island situated in Lake Mälaren. The island's greatest width is about 1.5 km (0.9 mi), it is about 5 kilometres (3.1 miles) long and covers 48 hectares (119 acres).
The island is perhaps best known for a major archaeological area. The old trading town on Helgö began to emerge around the year 200 AD, 500 years before Birka at Björkö. The first archaeological dig in 1954 uncovered the remains of the early settlement, including a workshop area which attracted international interest. The most notable finds included a small Buddha statuette from North India and a christening scoop from Egypt, both dating from the 6th century. The Indian Buddha statuette, the Irish crozier and the Egyptian Coptic scoop which were found on Helgö, are presently on display in the Swedish History Museum in .
The site where Kaggeholm Palace is located was first mentioned in a land title document in 1287. During the 1500s the farm was owned by members of the families Grip and Bååt. The farm was originally called Vettersjö, but was named by Swedish Count Lars Kagg (1595-1661) who bought the manor during 1647. Kagg was a political ally of King Gustavus Adolphus, a member of the Privy Council of Sweden and Field Marshal during the Thirty Years' War.
The château-style mansion was built in 1725 and designed by Nicodemus Tessin the Younger. Since 1939 it has been owned by the Swedish Pentecostal movement and is used as a training center by nearby Kaggeholm College.
The findings from the excavations at Helgö have been reported in a series of volumes published by the Royal Swedish Academy of Letters, History and Antiquities dating with Volume I covering the period 1954–1956. The most recent report was Volume XVII released during 2008.