The present municipality was created as recently as 1992, when Nyköping Municipality, which Trosa had been a part of since 1974, was split in three parts.
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. Being close to Stockholm, the municipality is a favourite amongst tourists from abroad. The well-equipped harbour and Trosa's archipelago also attract many pleasure boats from both Sweden and the other countries bordering the Baltic Sea.
Elections
The table below shows the results of the parliamentary (Riksdag) elections for Trosa municipality since the inaugural election under its current entity in 1991. 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.
The table below lists the relative strength of the socialist and centre-right blocks since 1991. Parties not elected to the Riksdag are included in "others" such as the Sweden Democrats (results from 1988 to 2006) and the Greens (1991). The sources are identical to the table above. The coalition or government mandate marked in bold formed the government after the election. The New Democracy party got elected in 1991 but are still listed under "other" due to the short lifespan of the party.
This is a demographic table based on Trosa Municipality's electoral districts in the 2022 Swedish general election sourced from SVT's election platform, in turn taken from SCB official statistics.[10]
In total there were 14,653 residents, of whom 11,006 were Swedish citizens of voting age.[10] 42.0% voted for the left coalition and 57.0% for the right coalition. Indicators are in percentage points except population totals and income.
