Københavns Amt
Vallensbæk is known from at least 1184 under the name "Wolensbech", possibly translating to 'narrow land area' or 'the field with the brook'. In the Middle Ages, when Denmark was divided into syssels, Vallensbæk was part of Østersyssel. It later became a part of Copenhagen Fief, which was changed to Copenhagen County in 1661. Although Copenhagen County changed many times over the years, Vallensbæk always remained within the borders. When the counties were disestablished in 2007, Vallensbæk came under the new Capital Region of Denmark.