The plaque, in memory of 25-year-old PC Norman Garnham, was provided by the Police Memorial Trust and has been placed on the courtyard wall of The Green Howards’ Museum in the town centre.
PC Garnham, who was killed on March 2 1977, was the first North Yorkshire Police officer to be murdered on duty.
Hitch-hiker Colin Simpson, 18, had run away from his home in Richmond after attacking his sisters.
PC Garnham pulled over to give him a lift, but when Simpson recognised him as a police officer, he ran off, but then stabbed PC Garnham as he tried to detain him.
Simpson was later convicted of murder and jailed for life.
At the time, the then chief constable, Robert Boyes described PC Garnham as “a police officer of the very best quality”.
Sergeant Amy Hunter, who is based in Selby, shares PC Garnham’s collar number and has worked with the Police Memorial Trust to establish the memorial.
She said: “I found out from a colleague that we both share the same collar number. At the time I felt saddened that I didn’t even know about Norman, and wanted to make sure that
everyone would remember his name, his service and the sacrifice he made for generations to come.”
Mrs Geraldine Winner, chairwoman of the Police Memorial Trust, attended the unveiling ceremony.
She said: “I am very pleased to be here in the beautiful county of North Yorkshire in place of my late husband Michael Winner to remember the service and sacrifice of Police Constable
“This is the 45th time the Police Memorial Trust have stood with the families of those officers who have died on duty to remember their loss.
“It’s absolutely right that the landscape of this garden should change just a little to accommodate our memorial to act as a permanent reminder to local residents and visitors alike of the life and death of Constable Garnham.”
Sgt Hunter and Assistant Chief Constable Phil Cain also attended the ceremony. Asistant Chief Constable Cain added: “We’re very pleased that there is now a fitting memorial to Norman in recognition of his selfless act on that fateful night in March 1977.
“Norman was murdered following an initial act of kindness that sadly led to his untimely death. We must never forget the sacrifice that he made and that such tragic events can happen anywhere, and sadly still do.
“Our thanks go to the Police Memorial Trust for providing the plaque and to Richmondshire District Council for their work to provide a peaceful but prominent site so that Norman’s family, friends, colleagues and members of the public now have a permanent and poignant place to remember him. Our thoughts remain with his family at this time.”
Julia Mulligan, Police and Crime Commissioner for North Yorkshire, said: “This is a fitting tribute to PC Garnham, whose selfless act to try to assist a member of the public in a time of need turned so tragic. He has been remembered at our memorial events each year, but having a specific plaque in his honour will remind many more about his service and sad, untimely death.
“The Police Memorial Trust have played an important part in this process, but Sgt Hunter deserves special credit and thanks for her tireless work in realising this poignant and touching memorial to PC Garnham, and for tracking down his family who continue to be in our thoughts today.”
A meeting room at North Yorkshire Police’s headquarters in Northallerton has been named after PC Garnham. Following a memorial service in May this year to remember all the force’s fallen officers and staff, Chief Constable Lisa Winward presented PC Garnham’s family with a canvas of a painting which hangs in the meeting room by local artist Gerald Hodgson.
The force also has two memorial gardens at police headquarters and Harrogate police station where fallen officers and staff are remembered.