Newly-elected members of the unitary authority, which takes full control of Northumberland next year, have backed calls already made by the Gazette to have the undisclosed sum made public.
Mr Henderson, a 44-year-old former Labour leader of Dundee District Council, announced his resignation to the Implementation Executive just three days before last Thursday's election.
A staff committee agreed the settlement terms but was legally bound by a confidentiality clause.
On Tuesday, we filed a new Freedom of Information Act request with the authority, following the rejection of an earlier bid last month, on grounds of public interest.
Yesterday, new unitary councillors added their weight to the Gazette pleas, which has already been backed by MP Alan Beith, prospective Conservative parliamentary candidate Anne-Marie Trevelyan and Labour MP for Wansbeck, Denis Murphy.
Alnwick's new Independent divisional member Coun Gordon Castle, said: "I wholeheartedly support these calls, and I will certainly be pushing for the figures to be made public.
"This whole saga needs to be put to bed, so that the new authority can move on from the old."
Rothbury's Liberal Democrat member, Coun Steven Bridgett, said: "What has happened is an absolute disgrace, because this is tax-payers' money which has been spent giving the chief executive a substantial golden handshake.
"The public has a right to know how much has been spent."
Amble West with Warkworth Independent Jeff Watson added: "Undoubtedly, these figures should be made public. This is a new administration and a new start for Northumberland.
"We have to get rid of all the skeletons in the closet."
Conservative member for Shilbottle, Trevor Thorne, said: "It's taxpayers' money and how it is spent should not be a secret."
Fellow party member Glen Sanderson, for Chevington and Longhorsley, added: "The spending of public money is everybody's business and therefore it would seem sensible and right to put these details into the public domain.
"Anything that appears to have been done behind closed doors raises suspicions."
Independent councillor for Longhoughton, John Taylor, said: "It's essential that the people who are paying these bills know how much it is costing them."
And new Labour group leader, Coun Grant Davey, said: "I would like to see the sum made public, but also how the whole series of payments to the chief executive came about.
"It should all be explained in public."
The county council has refused to be drawn on the issue, saying the details of Mr Henderson's severance package will remain confidential.