Harjumaa (Latin: Harria; German: Harrien) [1](1200 hides), was a historical county in Ancient Estonia until the early 13th century.

According to the Livonian Chronicle of Henry, Raikila was the main village of Harjumaa, where annual gatherings of the surrounding tribes took place.

Despite the name, the present-day Harju County covers only a small portion of the historical Harjumaa land, with most of its current territory corresponding to the ancient county of Revala.

Between the 10th and 12th centuries, one of the largest trading centers in Haarjumaa was the Varbola Stronghold (Latin: Castrum Warbole).

To secure a truce, Volkwin demanded that the inhabitants of Varbola accept Christianity and release their prisoners.