It comprises three municipalities: Hjartdal, Notodden and Tinn. The largest population centres in the region are the cities Notodden and Rjukan, of which Notodden is by far the largest with 8,319 inhabitants.  Hjartdal is scarcely populated.
The original municipalities in the district were Hjartdal, Tinn and Heddal, which were created in 1837 when the formannskapsdistrikt laws came into effect. In 1860 Gransherad municipality was created from portions of Tinn and Hjartdal. Hovin municipality was created by a split from Gransherad in 1886, and Notodden by a split from Heddal in 1913. In 1964 Heddal and Gransherad were incorporated into Notodden whereas Hovin was incorporated into Tinn. 
- Statistics Norway (2006). "Urban settlements. Population and area, by municipality. 1 January 2006". Archived from the original on 2006-08-21.
- Dag Jukvam / Statistics Norway (1999). "Historisk oversikt over endringer i kommune- og fylkesinndelingen" (PDF) (in Norwegian).
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