Sørfold is a municipality in Nordland county, Norway. It is part of the Salten traditional region. The administrative centre of the municipality is the village of Straumen. The old municipality of Folden was divided into Sørfold and Nordfold-Kjerringøy on 1 January 1887.
The municipality is named after the Folda fjord (Old Norse: Fold). The inner part of the fjord is divided into two arms Nordfolda ("the northern Folda") and Sørfolda ("the southern Folda"). The meaning of the fjord name is unknown (maybe "the broad one").
The coat-of-arms is from modern times. They were granted on 24 April 1987. The arms show a wheel of a turbine in a hydroelectric power plant. The streams around the municipality contained many rapids and waterfalls, which are partly harnessed to generate electricity. This has provided a major source of income for the community.