The Record Office in Chichester will be temporarily shut for two weeks from Monday December 3.
The closure, which happens every year, will help staff with major cleaning and sorting jobs as well as catching up on the backlog of cataloguing.
It will then reopen at 9.15am on Monday December 17.
Lionel Barnard, County Council Deputy Leader responsible for the Record Office, said: “The closure will help staff tackle the time-consuming jobs that cannot be completed when it is busy with members of the public.
“It will also allow the Record Office to continue to provide a high-quality service when it reopens.”
The temporary closure will have no effect on the registration and coroner services - both of which also occupy the building and will remain open as usual.
To find out more contact the Record Office on 01243 753 602 or visit Orchard Street, Chichester, PO19 1DD.
Alternatively visit its website at www.westsussex.gov.uk/recordoffice