The municipality consists of the following sub-municipalities: Wellen proper, Berlingen, Herten, and Ulbeek. Other population centres and hamlets include: Bos, Beurs, Kukkelberg, Langenakker, Oetersloven, Overbroek, Russelt, and Vrolingen.
Archaeological findings suggest the place was inhabited already during the Frankish period (5th to 7th century). Debris from the river Herk on that spot made fertile soil for farming. Mention of the name Wellene or Welnis doesn't occur until the second half of the 12th.
The name Wellen derives from the Middle Dutch "wellene", meaning "source" or "pit" or, alternately, from Latinterra Villina, "agricultural holding". Wellen was long associated with the abbey of Munsterbilzen, founded around 670.