Frederiksværk is a town with a population of 12,864 (1 January 2024)[2] in Halsnæs Municipality on Zealand in Region Hovedstaden in Denmark.

On 25 August 1756 the king issued a document permitting Classen to call the town "Friederichswerk".

Vinderød Church, in the town of Frederiksværk, houses the sarcophagus of General Classen and has a view towards the Arresø.

Displays in the museum concern weapon fabrication, gunpowder production and copper rolling during the years 1750 to 1900.

Asserbo Castle, which lies in the woods of Tisvilde Hegn, was founded by Bishop Absalon in the 12th century and was used as a monastery for monks of the Cistercian Order, originally invited from France.

The castle was reclaimed from the sands, first by King Frederik VII in 1849, and then by the National Museum of Denmark excavations in 1972.

Until 1 January 2007 Frederiksværk was also a municipality (Danish, kommune) in Frederiksborg County on the island of Zealand (Sjælland) in eastern Denmark, located between Lake Arre (Arresø) and Roskilde Fjord.

Its last mayor was Helge Friis, a member of the Social Democrats (Socialdemokraterne) political party.