Newly released figures from the Home Office show that in March this year, there were 13,030 licensed firearms in the area, up from 10,336 in 2009.
The number excludes shotguns, which are licensed separately.
It means there are 1,753 firearms for every 100,000 people in Lincolnshire, an increase of 19 per cent from March 2009, when local records were first collated. It is the highest rate at any point over the last decade.
In total, 4,174 valid firearm licences in Lincolnshire covered an average of 3.1 guns each.
There were a further 37,699 licenced shotguns in the area - a decrease on a decade ago.
Gill Marshall-Andrews, chairman of the Gun Control Network, said that society should be working towards fewer guns, and that the rise in legal firearms was difficult to explain.
She said: “We campaign strongly for tighter licensing laws and those have been introduced, by and large.
“It is becoming more difficult to get a gun licence, so I have no idea why it has gone up.
“Unless we are going to say that nobody should have a gun - and we have never said that - you should have a good reason to own a gun, and you should be a proper person. The guidance is stricter and the licencing regulations, if properly applied, should mean that fewer people have a gun.
“For years and years, the shooting lobby has said that gun crime it is just a matter of illegal weapons, but it is not true to say that gun deaths are related to illegal weapons alone.”
Between April 2017 and March this year, there were 293 new applications for firearm licences in Lincolnshire.
Of those, 96 per cent were granted, and just 11 were refused.
A further 904 licences were renewed. Just 13 licences were revoked.
The firearm rate in Lincolnshire was higher than that across England and Wales, where 578,000 firearms - 989 for every 100,000 people - were licensed.
In 2016-17, the most recent year for which numbers are available, there were 31 fatal shootings in England and Wales.
Altogether, there were nearly 10,000 offences in which firearms were reported to have been used.
Of those, 33 took place in Lincolnshire.
Many gun crimes involve the use of illegal firearms either weapons converted to fire live ammunition, or restored antiques.
But some high-profile cases, including the murder of MP Jo Cox in 2016 - which was carried out with a stolen gun - and mass killings in Cumbria, Dunblane and Hungerford, have involved licensed weapons.
A spokesman for the National Police Chiefs’ Council said: “It is the responsibility of individual forces to issue firearms certificates, and there are several reasons why the number of legally-held firearms may have risen in the last decade, such as changes in legislation. Therefore, the increase in the number of legally-held firearms is not necessarily a cause for concern.
“The Home Office is constantly monitoring the types of weapons that are held on and off certificate and consult on changes to legislation when required.
“Only a tiny percentage, something in the region of 0.025 per cent, of legally-held firearms goes missing each year, and that is when they become a significant concern for police.
“The Home Office and local police forces provide guidance on the appropriate storage of firearms and ammunition to certificate holders and are continuing to work to ensure that this already small number of missing weapons is reduced further.”