Although the original county was still quite small - and limited to the territory between the Dender and Zenne rivers, situated to the west of Brussels - from the 13th century onwards its name came to apply to the entire territory under control of the dukes.
Kuigi algne krahvkond oli ikka veel üsna väike ja piiratud territooriumiga Denderi ja Zenne jõgede vahel, paiknedes Brüsselist läänes, kasutati 13. sajandist alates selle nime kogu hertsogite kontrollialusele territooriumile.