The 1st Kettering Scout Group is inviting former members to a special troop meeting in September.
Group leader Chrissie Brant said: "If we can pull it off really well, it's going to be fantastic."
Older members who have already been contacted h
ave agreed to come, but only if there is a camp fire.
Mrs Brant, from Kettering, said: "Everyone from the seven-year-old Beaver to the 70-year-old former member can be involved with a camp fire."
The group has about 100 members and has the names and addresses of 300 former members from as far away as Canada.
Former members of all ages, including an 82-year-old who was a Scout in the 1930s, have already said they will be attending.
Mrs Brant said: "Most people we have spoken to have said: 'When? Where? I will be there.'
"I'm hoping we will get them all there. We would love to get up to 500. We are all still Scouts, no matter what."
They are planning to have a hog roast and there will be a chance for previous members to catch up.
New centenary flags for the Beavers, Cubs and Scouts will also be dedicated at a church parade on the Sunday.
Mrs Brant and Scout leader John Hopkins had done some digging into the group's history, but it was only when they requested the group's records from the central office in Gillwell, Essex, in February that they found out it was their centenary.
Mrs Brant said: "There has always been the story that we must have been one of the first Scout groups but it was not until we went to Gillwell that we could prove it with hard evidence."
The group would also like to hear from people with stories or photographs about their time in the Scouts.
For more information about the event, to be held on Saturday, September 12, contact Mrs Brant on 01536 390601.
