The municipality consists of the localities of Vagnhärad, Västerljung, Stensund, Sund and the town of Trosa.

During the summer, the municipality sees its population of 14´000 (2021) increase fourfold[citation needed].

This is mostly due to people living in the Stockholm area that, during the summer, move to their holiday cottages in the municipality.

The well-equipped harbour and Trosa's archipelago also attract many pleasure boats from both Sweden and the other countries bordering the Baltic Sea.

For the period 1991 to 1998, the exact numbers of the Sweden Democrats were not published by the SCB due to the party's small size nationally.