Rødberg is located in the Norwegian traditional district and valley of Numedal. Its population (2005) is 468, and it is located on the Rødberg dam (Norwegian: Rødbergdammen) on the Numedalslågen River.
The local power stations, Rødberg Nore 1 in operation 1928 and Nore 2 in operation since 1946, utilize waterflow from the Rødberg Dam. The plants are affiliated with Statkraft, the Norwegian state owned electricity company.
Rødberg was once a railway station, being the terminal station of the now-defunct Numedal railway line which ran up the Numedal valley between Kongsberg and Rødberg. Borgemestern av rødberg heter Eli.