The Museum building was constructed in stages between 1865 and 1882. It housed the Telegraph Office from 1865 and then the Wollongong Post and Telegraph Office from 1870 until 1892. At the time that the building was erected, Market Square was the commercial centre of Wollongong due to its proximity to the harbour.
The Telegraph Office was completed in 1865 at a cost of £670. It had a single storey and a shingle roof with a central foyer. The telegraph office was on the on east side with a separate transmission room now used as a staff kitchen. The Telegraph Station Manager, Richard Willis, was appointed in 1862.
In 1869 a tender was let for building extensions in order to accommodate the post office. The work involved the addition of three western rooms – post office, mail room (now the stairwell) and the Post Master’s Office. At the same time, work was undertaken on the eastern side to extend the Telegraph Office by joining it with the transmission and battery rooms. In 1870, Philip Mackel was appointed Master of the Post and Telegraph Office.
The Colonial Architect drew up plans in 1880 for the upper storey and the work was completed in 1882. The new space provided living accommodation for the Post Master and his family. In 1885, a new battery room was built on the western boundary.
The construction of the railway hastened the development of Crown Street as the commercial centre of the town. In 1888 Francis Woodward MP made a suggestion that a new Post Office be built in Crown Street. The new Post Office was completed in 1892 adjacent to the Town Hall. The former Post Office became the offices of the Wollongong Harbour Trust until the Trust folded in 1895. The Department of Public Works assumed control of the building and it was used by a variety of government offices including the Dole Office that distributed food and clothing relief during the 1930s Depression. During the Second World War the Recruiting Office used the building and a brick air raid shelter was built. Tenants after the War included the Electoral Office 1946-47, Motor Registry 1947 to 1964 and the Department of Labour and Industry till 1966.
Control of the building passed to the Wollongong City Council in 1966 and the ground floor rooms were offered to the Illawarra Historical Society for use as a museum. The Electoral Office continued to use the air raid shelter for storage, the Civil Defence Organisation occupied two upstairs rooms and the other rooms upstairs were leased as a flat.
The Society was the sole tenant by the end of 1968 and commenced a programme of adding buildings in the yard. The blacksmith’s shop was opened in May 1972, and the first stage of the farm shed commenced in 1979. A storeroom and the southern part of the farm shed were added in 1983.
Ownership of building transferred to Wollongong City Council in 1978 and the National Trust of Australia classified the building in 1985. The building was added to the NSW Heritage Register in 2016.