Three years after the very first WI was set up in 1915 in Wales, 13 WIs were formed across Northamptonshire.
Of those trailblazers, six remain – the WI in Brackley, along with Brigstock, Wootton, Badby and Fawsley, Clipston and Hargrave – making them some of the oldest groups in the country.
Sue Kendall is the federation chairman for Northamptonshire and she said it was a triumph for women that the WI continues to exist.
She said: “To make it to 100 years is an unbelievable achievement.
“It’s an amazing feat for a women’s organisation to have got so far and it coincides with 100 years of women getting the vote.
“The WI was set up in Canada by a woman whose young son died from drinking contaminated milk.
“She was wanted to educate women on agriculture issues and it just grew from there.
“The mission of the WI is all about educating women.”
Northamptonshire has more than 120 groups with about 3,700 members.
The county has got behind national resolutions the WI has campaigned for.
These have included allowing parents to stay with children in hospital, Keep Britain Tidy and the price paid to farmers for milk.
In more recent years, it has taken part in the WI’s focus on tackling loneliness and the bid to reduce plastic polluting the world’s oceans.
The celebrations will also include trustees of the county federation visiting each of the six WIs marking their centenaries.
The federation’s all-day AGM at Kettering’s Lighthouse Theatre in November is also set to be a grand celebration, with talks by cookery author William Sitwell and television presenter Kate Humble.
Throughout the year, there will be a number of centenary items on sale along with the reproduction of a 1933 WI cookbook.