The service takes place on Tuesday 21 February 2017 at 3.15pm.
Mrs Johnson was a member of the County Council from 1981-2009 and served as the Council’s Chairman for seven years, the longest tenure of Chairmanship for the last 40 years.
Residents are invited to join the County Council in paying their respects to Mrs Johnson and her family.
The current Chairman of West Sussex County Council, Pat Arculus, said: “The County Council is pleased to be joining Mrs Johnson’s family for a service of thanksgiving.
“Margaret made a significant contribution to the county as our first female Chairman and this service will be a fitting tribute to her and all that she achieved in her life.
“Margaret was heavily involved in a number of charities and public organisations, including the Sussex Community Foundation and St Wilfrid’s Hospice, as well as being a Deputy Lieutenant for West Sussex.”
Mrs Johnson died in November 2016.
Residents are asked to please use local public car parks when attending the service.
Credit: Photo of Margaret Johnson courtesy of the Chichester Observer