Nykvarn Municipality (Nykvarns kommun) is a municipality in Stockholm County in east central Sweden. Its seat is located in the town of Nykvarn.
Nykvarn is a young municipality, and is the result of the splitting of Södertälje Municipality in 1999. Nykvarn can be regarded as a totally new municipality, because there was never before an entity with that territory or that name.
The municipality has a significant population increase in the summer thanks to tourism.
Nykvarn is located between the two cities Södertälje and Strängnäs, and many citizens of Nykvarn work in either.
Archeological finds show the area to have been inhabited for about 5,000 years, similar to its neighbouring municipalities around Lake Mälaren.
Besides graves from the Stone Age, there is also an interesting runestone that can be visited that is listed in the Rundata catalog as Sö 338. It currently resides in the Turinge church, a church that has a history dating back to around the year 1100. This runestone has