The first part of the name comes from the Old Norse word Ó or À, which means 'river' (here referring to the Glomma river).

Traces of human habitation dating back to the Nordic Bronze Age, between 1500 and 500 BCE.

Increased mobility in the Norwegian population likely changed the character of the society in Odalen, and there is evidence the area was under the administration of the Thing in Eidsvoll.

[4] When the region was Christianized around 1030, several churches were built, including locations at Oppstad, Strøm, Ulleren, Mo and Trøftskogen.

The valley may have become overpopulated until the Black Death and following plagues, when a huge proportion of the population died.