The remarkable discovery was made by Steven Ingram, who was searching a ploughed field near the village.
The coins were scattered throughout the soil, but fragments of the pot they were originally contained in were found nearby.
Dr Adam Daubney, finds officer for the Portable Antiquities Scheme at Lincolnshire County Council, said: “This is a monumental find from the turbulent years of the English Civil War. The latest coin in the hoard shows that it was buried early in 1643 – just months after the war broke out.
“The total value of the hoard – in terms of when it was buried – comes to just over £34. To put that in perspective, an infantry man in the Civil War earned about a shilling a day, while a gentleman could easily live off £20 a year. So this is a significant sum of money,” he said.
“This is the largest of the hoards that has been found from that time in the county, and it contains coins from the reigns of Edward VI, Elizabeth, Mary, James I, and Charles I.
“The area between Grantham and Boston was a zone of intense conflict between the Parliamentarians and the Royalists in the early years of the war, so we can think of the Ewerby hoard as being from the ‘front-line’.”
He went on: “The hoard tells us about the uncertainty and fear that must have been felt at the time, but quite why it was buried – and by whom – is impossible to say. It might have been buried by someone who went off to fight and never returned. Interestingly, several of the estates that lay close to the site of the hoard were fined after the war for supporting the King.”
The land is owned by local farmer Chris Sardeson, who said: “I’ve worked this field for more than 50 years, so no-one is more surprised than me!”
The hoard is being processed under the Treasure Act, and a report on the coins is currently being prepared for the Coroner who will make a decision on ownership and proceeds.