The new archives centre cost £8.2m
The records office at Carlisle Castle will close at the end of next month, it has been confirmed.
More than a million historical documents will be moved to new premises at Petteril Bank.
County archivist Anne Rowe described the new building as "iconic" and said alternative research services will be offered during the changeover.
The new facility, known as the Cumbria Archives Centre, will open to the public in January 2011.
Anyone wishing to access records in the meantime should contact Cumbria County Council.