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.
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 a very long inscription.
A newer sight is the Taxinge-Näsby Castle, which was begun sometime in or before the 14th century, by Bo Jonsson Grip. The castle has its current facade in the empire style from 1813. Many celebrities have during the centuries visited or stayed at the castle, including Carl Michael Bellman in the 18th century and August Strindberg in the 19th century.