Five of those injured at the event at Ripley Cricket Club were taken to Harrogate hospital while another was taken to Leeds General Infirmary suffering from chest pains.
A North Yorkshire Police spokesman said no one was thought to have been critically injured.
"Officers have seized the slide and investigations are continuing at the scene," he said.
"The Health and Safety Executive has been informed and are also attending the scene of the incident."
Witnesses said they saw the inflatable roll over people and stalls.
The Harrogate News reports: "Witnesses described seeing the slide being blown in strong winds around 50 metres, over the top of an AA van, before coming to rest."
Carmen Williams, who was at the scene and took this dramatic photograph said, said: "I was sat there in the cafe and in a flash the bouncy castle with two or three children on it just flew over.
"People were screaming and running away from it. It was awful."
She said two of the injured people were elderly; one woman was hit on the head by the inflatable.
The land is part of the Ripley Castle estate.
On Ripley Castle's Facebook page a message said: "Our sympathy to all those affected by the bouncy castle incident at the Ripley Cricket Club car boot sale on the cricket ground this morning: hope those injured make a swift recovery.
"The latest information that we have been given indicates that none of the injuries are serious, thank heavens: one person being detained in hospital for observation, just to be certain.
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