Organisers of the two-day Woodhall Spa 1940s Festival said last weekend the event would not take place next July due to "rising operating costs".
They said in a statement on social media they had alerted police to a "possible criminal offence".
Lincolnshire Police said the investigation was at an early stage.
A police spokesperson said: "Lincolnshire Police is investigating an allegation of fraud.
"As the enquiry is in its early stages it would be inappropriate to comment further at this stage and we will keep the public updated as and when we can."
The Woodhall Spa Committee issued a statement confirming the investigation on social media today.
They said: "Our team is currently liaising with Lincolnshire Police after the committee alerted the authorities regarding a possible criminal offence.
"As this is an ongoing investigation, we can make no further comment at this time".
The free event, which featured shows and military reenactors, as well as flying displays across the weekend, was first held in 2012 and attracted thousands of visitors.
The Woodhall Spa Committee said last weekend "the costs of keeping so many people safe [and] well served... have risen very sharply".
As they did not expect costs to come down in future years they believed it was time to "say a fond goodbye".
The leader of East Lindsey District Council Craig Leyland, who represents Woodhall Spa, said the festival had been a major contributor to the area's economy over the last decade.
"People have put an awful lot of effort into this, the organisers, the businesses that take part and of course the visitors who come to enjoy what we have to offer in Woodhall Spa.
"This investigation, the news of it is just incredibly sad news."
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Police have confirmed an investigation into an allegation of fraud connected to a popular wartime-themed festival in Lincolnshire has begun.