Approximately 875,000 paying guests passed through the tenth century landmark last year, compared to nearly 1,070,000 in 2007.
Bosses believe the slump has been particularly stark since the Charlie Hebdo attack in 2015 when two brothers forced their way into the Paris office of a satirical newspaper and killed twelve people.
Director of visits and marketing at the cathedral, Therese Heslop told Kent Online: "Visitor numbers have gone down ever since Charlie Hebdo, and terrorism continues to affect the tourism industry, and especially major tourist attractions."
Canterbury Cathedral was ranked at the 19th-most visited attraction in the UK ten years ago. By last year, it had slipped to 43rd.
Therese Heslop went on to say: "In terms of money, we are talking [about a loss of] between £200,000 and £250,000 a year."
Visiting school children from continental Europe have traditionally been a major source of revenue for the World Heritage Site, comprising of a quarter of all paying guests.
Yet, 30,000 fewer youngsters in groups visited Canterbury Cathedral last year compared with 2014.
Voicing some optimism around growth in adult group visitors, Heslop added: "The American market is strong and our status as Mother Church of the worldwide Anglican Communion and part of Canterbury's World Heritage Site continues to attract visitors from all over the world."
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