The parish of Hedrum was established as a municipality on January 1 1838 (see formannskapsdistrikt). Small parts of Hedrum were transferred to the city of Larvik in 1855, 1875, 1937 and 1948. Border adjustments between Hedrum and the neighboring municipalities Andebu, Tjølling and Siljan also took place. Hedrum was incorporated into the enlarged Larvik municipality on January 1, 1988. Before the merger Hedrum had a population of 10,449.
Hedrum located in Lågendalen, the lower part of the valley that follows the river Numedalslågen. The valley is relatively flat, dominated by agricultural areas, valleys are wooded hills and go over the mountain peaks up to 500 meters. Among other things, the area is known for potato cultivation and fishing.
Hedrum Church was built of stone around 1100 and has 260 seats. In 2010 the church celebrated its 950-year anniversary during 2010. The church has a rectangular nave, square choir and apse. Building Archaeological studies show that the apse is added later. The structure was extended by four meters in 1666 . The west part with the portal and door openings are from after the Reformation. Hedrum Church has a number of tombstones, which cover large parts of the floor of the church. Hedrum Church cemetery is clearly visible from traffic arteries on both sides of Numedalslågen. Some of the graves are believed to pre-date the introduction of Christianity confirming the supposition that ancient pagan cult sites were chosen as the venue for the earlier churches. 
The municipality (originally the parish) was named after the old farm Hedrum (Norse Heiðarheimr), since the first church was built there. The first element is the genitive case of heiðr f 'heath, moor', the last element is heimr.
- Ekroll, Øystein; Ladder, Morten; Havran, Jiri; (2000) Middelalder i Stein (Volume 1 of the series Kirker i Norge) ISBN 82-91399-09-3
- Nyhus, Per (1999) Larvik A-Å (Larvik: Østlandsposten) ISBN 82-990835-3-2
- Krohn-Holm, Jan W. (1982) Hedrum bygdebok (Larvik: kulturhistorie)
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