 Frederikssund's rapid expansion from a small town at the end of the 19th century is due in large part to the railway connection with Ballerup in 1879 which was upgraded to a frequent suburban service to Copenhagen in 1989.Frederikssund is located on the east coast of Roskilde Fjord, about 45 km north-west of Copenhagen, 20 km south of Hillerød and 30 km north of Roskilde.It is less than an hour from Copenhagen by either road or rail.