Dunster Castle – a favourite destination for tourists from all over the world
Historic properties, such as Corfe Castle in Dorset, are attracting thousands more visitors each year, according to figures from VisitBritain.
The survey showed Britain's monarchy-related attractions generate more than £500 million a year in overseas tourist spending.
Culture and heritage generally, including theatres, galleries and pubs, helped raise £4.6 billion in money spent by foreign residents last year, the report added.
VisitBritain chief executive Sandie Dawe said: "This fascinating research shows Britain's monarchic heritage draws foreign tourists to just about every corner of the country, from Scotland to Cornwall.
"The Queen celebrates her diamond jubilee in 2012, a feat last accomplished back in 1897 by Queen Victoria. This report suggests that year she is going to generate a bonanza for British tourism."
Of the 30 million overseas visitors who came to Britain last year, 5.8 million visited a castle, five million an historic house and 6.4 million a religious monument such as a cathedral.
The Tower of London was the top royal attraction for international visitors in 2009, with just under 2.4 million visitors, while the top West site was Corfe Castle, which was visited by about 199,900 people, up 23 per cent on the previous year. Allan King, Wessex regional communications manager for the National Trust, said overseas visitors were very important to the organisation.
"We find they love discovering the connections between royalty and historic properties, the type of stories which help to bring life to a tour of a historic place.
"Popular attractions include Dunster Castle and Corfe Castle, built by William the Conqueror and greatly developed by King John.
"The latter was an important Royalist stronghold until it was blown up in the civil war. Despite not being on the main tourist routes from London to Stratford, about a quarter of visitors are from overseas, mainly Europeans with some visiting from cruise ships docked in Poole Harbour.
"These castles are popular with visitors from across the world but we also find the royal connections fascinate people in the South West."
In a VisitBritain-commissioned survey of 25,000 potential visitors to Britain, nearly three-quarters said they would be likely to visit a castle or stately home and 60 per cent said they would be likely to seek out places associated with the Royal Family or British monarchy.