The State Archives and Records Authority of New South Wales has a huge collection of historical records. They are charged with managing, preserving and providing access to the states archives. The NSW State Archives stores records for the New South Wales public sector.
The body is covered under the State Records Act of 1998.
Information is made available to the public through the website and in person. You can conduct a wide range of searches online and request copies of the physical documents in person. Some digital copies have also been made available.
Some of the more popular categories they provide records for include:
This is just a small example however as the NSW State Archives houses a huge range of information, some 640km worth in physical terms.
An alphabetical index of all topics covered is the easiest way to get started. You can also try the site search for the records you are seeking.