The Queen and Duke of Edinburgh were shown around a £19 million state-of-the-art resource centre.
HRH Queen Elizabeth officially opened The Keep, near Falmer, which will provide a home for archives and historical resources of East Sussex and Brighton and Hove.
Archivists showed the royal delegation maps of Sussex and historic pictures of Eastbourne before it became a resort.
Other archives included photos of Brighton Carnival stretching along Madeira Drive and its oldest document, Battle Abbey Charter, from 1101.
Senior archivist Chris Whittick said: “They both showed a great interest in what he had shown them and they made most perceptive comments.
“We tried to select documents that would be of interest but not too personal. I think we got the right balance.”
Around two hundred royal watchers waited at Woollards Field, Moulsecoomb, for the royal cavalcade to arrive.
The party met with officials including the leaders of East Sussex County Council Keith Glazier and Brighton and Hove City Council Jason Kitcat.
The Duke of Edinburgh was impressed by the technology used to store artefacts.
The technologically-minded Prince set up Buckingham Palace’s filing system, a royal aide said.
Members of the Women’s Institute showed the Queen historical bags made by their predecessors.
As the royal party was shown around, cheerful crowds waved Union Jack flags.
Alessia Briante, 41, of Moulescoomb, said: “I first met the Queen in 1999. I moved here from Naples in Italy many years ago. My daughters were born here. This is home for us. She feels like my Queen.”
Sally Woolard, 67, Cross-in-Hand, said: “My husband’s family own the land the Keep is built on. It’s a great day for us.”
Ernie Townsend, 90, Brighton, WWII Veteran, said: “I was on the guns at Normandy, and a bricklayer thereafter. I saw the Queen once, a long time ago though.”
Joy Allsop, 70, Chesterfield in Derbyshire, added: “It’s a big day for me. I’m a royalist through and through.”
Terry Killick, 76, Woodingdean, said: “I met her once in the 70s. I’ll be damned if she or I remember it though!”
The Keep, which is due to open to the public soon, will be a portal for the public to trace the history of their local community through documents dating back 900 years.
The cost of the new building is split between councils, with two-thirds of the building to be used by East Sussex County Council and one third for Brighton and Hove City Council.
The University of Sussex has also contributed £1 million.