Guernsey Museum in Candie Gardens had 40% more visitors during the summer of 2010 than the same period in 2009.
Before November, 17,470 people had seen exhibitions including the BBC's A History of the World and Wildlife Photographer of the Year.
Guernsey Museums director Jason Monaghan said: "I am very pleased with the way the season has gone and the support of islanders and visitors."
He said other venues run by the States had also had more visitors.
Mr Monaghan said: "2010 is shaping up to be the best season this side of the millennium."
He said the most popular exhibition at the Candie Museum was Occupied Behind Barbed Wire, which showcased arts, crafts and domestic items made by Channel Islanders deported to internment camps during World War II.
It was seen by an estimated 12,000 people.
He said Castle Cornet had welcomed exactly 47,000 visitors at the end of October, which was a rise of 2,000 on the summer season of 2009, and both Fort Grey and the Telephone Museum experienced increases.
Mr Monaghan said: "Other heritage sites sometimes overlooked, such as Grande Rocques battery, Mont Chinchon and Fort Hommet see a regular stream of people exploring the sites or simply enjoying the views.
"These sites are among the 75 that the Museum Service cares for, and which are free to for all to see and admire."