The municipality consists of several former local government units and was formed in 1971. It got its name from the small, but very old, City of Sigtuna, but the seat was placed in the larger modern town of Märsta.
The three towns of the municipality are Märsta (pop. 23,000), Sigtuna (pop. 8,000) and Rosersberg (pop. 1,400), of which Märsta is the municipal seat and Sigtuna with its old and important history is a popular tourist destination.
In the municipality lies the largest workplace in Sweden, the Arlanda Airport, with 13,000 employees in 200 companies. As a result, Siguna is travelled through by 18,300,000 visitors yearly, and has the fourth most hotel stays, following to the commercial and regional centres Stockholm, Gothenburg and Malmö.