Hiiu County (Estonian: Hiiu maakond or Hiiumaa) is one of 15 counties of Estonia, being the smallest county both in terms of area and population. It consists of Hiiumaa (German and Swedish: Dagö), the second largest island of Estonia, and several smaller islands near it. The county borders Lääne County to the east and Saare County to the south.

Human habitation of Hiiumaa can be traced back to the fifth millennium BC. Mesolithic sites in Kõpu peninsula are exemplified by the seal-hunters' settlements. There are several well-preserved grave fields of the Iron Age. The island was first mentioned in 1228, in annals written under the name Dageida. In 1254, Hiiumaa was divided between the Livonian Order and the Bishopric of Ösel-Wiek. In 1563 Hiiumaa was annexed into Sweden. In 1710, as a result of the Great Northern War the island went under the control of the Russian Empire. During World War I, the German military forces occupied Hiiumaa in 1917. In 1918–1940 Hiiumaa was part of the Republic of Estonia, then until 1991 occupied by the Soviet Union.

On demands of the Hanseatic League a lighthouse was built in Kõpu (previously known as Dagerort) at the beginning of the 16th century. It is considered the third-oldest continuously operating lighthouse in the world, still showing its light to 35 miles (56 km) of the sea.

Most of the farm architecture comes from the 19th century. Prominent examples include the Mihkli farming complex and Soera farm-museum with historical national artifacts, respectively.

Most important sights:

• Suuremõisa manor
• Kõpu Lighthouse and ancient graves
• Suursadam port
• Tahkuna Lighthouse and associated coastal defenses
• Ristna Lighthouse
• Sääretirp
• Saarnaki laid and other isles
• Kärdla town
• Käina church ruins
• Ristimägi hill [et]
• Reigi church
• Kärdla meteorite crater
• Kassari chapel, Kassari

The County Government (Estonian: Maavalitsus) was led by Governor (Estonian: maavanem), who is appointed by the Government of Estonia for a term of five years. The last Governor was Riho Rahuoja 2012−2017.

Religious affiliations in Estonia, census 2000–2021*

Religion	2000		2011		2021
	Number	%	Number	%	Number	%
Christianity	1,439	17.7	1,167	16.0	960	12.9
—Orthodox Christians	88	1.0	91	1.2	170	2.3
—Lutherans	972	12.0	790	10.8	560	7.3
—Catholics	8	0.1	6	0.08	20	0.2
—Baptists	319	3.9	182	2.5	120	1.6
—Jehovah's Witnesses	25	0.3	23	0.3	30	0.4
—Pentecostals	13	0.1	9	0.09	-	-
—Old Believers	1	0.01	1	0.01	-	-
—Methodists	3	0.03	3	0.04	-	-
—Adventists	10	0.09	5	0.06	-	-
—Other Christians	-	-	57	0.7	60	0.8
Islam	-	-	1	0.01	-	-
Buddhism	-	-	4	0.04	-	-
Other religions**	65	0.8	78	1.0	70	0.9
No religion	3,183	39.2	4,903	67.2	5,450	73.2
Not stated***	3,418	42.1	1,124	15.4	910	12.2
Total population*	8,105		7,291		7,440
*The censuses of Estonia count the religious affiliations of the population older than 15 years of age. ".

The county consists of one municipality after the administrative reform of 2017. Between 2013 and 2017 the county was subdivided into 4 municipalities (Estonian: vallad – parishes). The only urban settlement Kärdla is part of Hiiumaa Parish since 2017.

Rural municipalities:

• Hiiumaa Parish (includes the town of Kärdla)

The county includes the islands of Hiiumaa (980 km (380 sq mi)) and Kassari (19 km (7.3 sq mi)) and a number of surrounding islets. The highest point is Tornimägi hill (68 m (223 ft)), the longest river is Luguse (21 km (13 mi)), and the biggest lake is Tihu Suurjärv (85 ha (210 acres)).

In the landscapes there can be found pine forests, mixed spruce and deciduous forests, swampy thickets and juniper shrubs, coastal meadows and bogs. The most frequent tree is pine which makes about a half of forests. Pine is followed by birch, spruce and alder. In total, there are about 1,000 species of vascular plants, of which about 100 are under protection. The wildlife of Hiiumaa is remarkable. Out of 30 species of mammals, big game as elk, deer, fox, wild boar and lynx roam the island. There are about 250 species of birds on the island, 195 of them nesting.

Among the Estonian counties Hiiumaa is the richest in forest – nearly 60% of the island are wooded areas. There are large marsh areas in the middle of the island. The marshes cover about 7% of its area. Cultivated land and settlements take about 23% of the area of the county.

• Lääne-Viru County Government – Official website
• Lääne-Virumaa County Infoserver – map and tourism info Archived 28 March 2010 at the Wayback Machine