As part of the £7,000 investment, existing defibrillators in SKDC's Customer Services area and the Guildhall Arts Centre will also be moved outside so they are accessible 24/7.
A defibrillator gives a high-energy electric shock to the heart to someone who is in cardiac arrest and plays an essential role in helping to save lives.
SKDC's Cabinet Member for Communities, Health and Wellbeing, Cllr Robert Reid, said: "Installing these defibrillators is a perfect fit with our commitment of supporting the wellbeing of our local communities.
"With Grantham being such a busy town, it is a no-brainer to have such important lifesaving equipment easily available at several locations, yet to be decided.
"While we all hope they won't have to be used, it is reassuring for people to know they are there if required.
"The reality is that increasing the number of defibrillators can make the difference between life and death and ultimately give people the chance to spend more time with their loved ones that they might not otherwise have had."
The need for more defibrillators was highlighted by Grantham St Vincent's Councillor Charmaine Morgan.
"There is a need for defibrillators in the town centre and in all our residential areas and estates where gaps exist," she said.
"The issue has been raised with me by street pastors, who help late night revellers at weekends, and the LIVES emergency responders, who say they should be available 24 hours.
"Once installed they become part of the 999 network so that if people call 999 in an emergency they will be told where to find their nearest defibrillator."
The defibrillators will be in easily-recognisable boxes on the outside walls of buildings to make sure they are always accessible.