Hiiu County, or Hiiu maakond, is a County or maakond of Estonia. Hiiumaa is the second largest island of Estonia and constitutes the main part of the county. It is located in the Baltic Sea to the east of Lääne County on the mainland, and to the north of Saare County.
The county includes the islands of Hiiumaa (980 km²) and Kassari (19 km²) and about 200-400 surrounding islets. The highest point is Tornimägi hill (68 m), the longest river is Luguse (21 km), and the biggest lake is Tihu Suurjärv (ca 85 ha).