The collection of the Hiiumaa Museum originated from the local history collections of Leisu School and Mänspäe School, which were almost entirely transferred to the local history museum when it was being founded. The founder of the first museum in Hiiumaa was Volli Mäeumbaed, a local history enthusiast and school teacher. On his initiative, the Hiiumaa Museum was opened on 28 May 1967 in the house of the field hands of Kassari Manor. As of today, there are more than 34,000 museum objects in the collection of the Hiiumaa Museum. 

The objects received from the local history circles of Leisu School and Mänspäe School, which had mainly been brought by the local children, caused the peasant culture represented in the museum collection to be swayed heavily towards southern Hiiumaa. Later, an attempt has been made to find objects missing from the ethnographic collection from other regions of Hiiumaa as well. One of the rarest objects in the ethnographic collection is a wooden milk pail, which has the year 1510 carved under its bottom. It is one of the oldest dated wooden vessels in Estonia. 

The objects in the historical collection are predominantly of industrial kind and made of various materials in different eras. The versatile collection includes furniture, tableware, radios, musical instruments, liturgical items. Objects particularly worth highlighting in this collection are a silver jug with the coat of arms of the Ungern-Sternberg family, the bagpipes of Juhan Maaker, and Estonia’s biggest collection of wide-seated rocking chairs.  

The textile collection includes, in addition to the clothes worn by the Hiiumaa people, household items made of textile, accessories, shoes, and flags. Those interested in folk costumes can view the original items in the Long House, which also houses the Hiiumaa Folk Costume Advisory Council. 

The art collection has some works from almost all artists who are Hiiumaa natives. The works of Ülo Sooster from his youth are particularly valuable, but art by Aarne Miikmaa, Kaljo Põllu, Paul Kamm, Ott Lambing, and others is also represented. The archive collection of the Hiiumaa Museum has over 6,000 museum objects presenting the daily life of the Hiiumaa people. The most valuable parts of this collection are the economy diary of Otto Reinhold Ludwig von Ungern-Sternberg, the archive of the Society of Hiiumaa Natives in Canada, slips with the Hiiu dialect, and Arnold Sergo’s archive. 

The photo collection provides a good overview of Hiiumaa in the 20th century. The biggest asset of the photo collection is the collection of glass plate negatives that belonged to Ernst Otto Adam von Ungern-Sternberg, the owner of the Kärdla Broadcloth Factory. Starting from 2022, the museum also opened a digital photo collection, where only the museum objects in digital format are stored. 

The various branches of the museum have also contributed to the overall look and feel of the collections. 

• Starting from 1973, the birth home of Rudolf Tobias, one of the founders of Estonian concert music, located in Käina, belongs to the Hiiumaa Museum. 

• Starting from 1987, the museum owns a rare example of Northern European architecture – the farm building ensemble of Mihkli farm in Malvaste Village.
   
• In 1988, the Hiiumaa Local History Museum inherited Kroogi farm – a unique dwelling ensemble from the 1930s in Valgu Village. It belonged to a family affected by the Communist deportation.
   
• Starting from 1998, the Long House – the former residence of the directors of the Kärdla Broadcloth Factory – has been the museum’s main building. All this has enabled the Hiiumaa Museum to present the past and the present day by means of museum buildings, objects, and locations. 

 The collections of the Hiiumaa Museum are intended for research, for providing ideas for new creations, for putting together exhibitions, for educational and other inspiring activities.