Bernard Kenny, 78, was stabbed as he intervened when Thomas Mair attacked Mrs Cox in his home village of Birstall, West Yorkshire, a year ago.
PCs Craig Nicholls and Jonathan Wright - who arrested Mair - have also received Queen's Gallantry Medals.
Unarmed, they pursued him despite knowing he may have a gun and a knife.
The late politician's senior caseworker, Sandra Major, who witnessed the killing, receives an MBE for parliamentary services and service to the community in Batley and Spen.
Mrs Cox, the Labour MP for the Yorkshire constituency of Batley and Spen, was stabbed and shot outside Birstall Library on 16 June 2016.
After the attack more than 80,000 people signed an online petition calling for Mr Kenny to be awarded the George Cross for his bravery.
At Mair's trial at the Old Bailey, the jury heard Mr Kenny was waiting for his wife outside the library in Birstall when he saw Mair going "berserk".
He said in statement to police: "I thought if I could jump on to the back I could take him down.
"I thought he was thumping her until I saw the blood. I saw he had a knife in his hands.
"Just as I got short of him, he turned around and saw me. He shoved the knife in and it hit me in the stomach. The blood started pouring out between my fingers. I saw the blood and I thought 'Oh my God'."
Mr Kenny said: "I am honoured to receive such an award."
After the attack, Mair left the scene armed with a knife and a gun and was followed by PC Nicholls and PC Wright.
Realising the public could be in danger, the officers chased the suspect and arrested him.
'Heroic actions'
PC Nicholls said he was "honoured, surprised and humbled" to receive the gallantry award.
"Our thoughts remain with Jo's family and friends. We have met members of her family who are incredible and extremely positive.
"On the day this happened, we were not due on patrol but our training was cancelled.
"When we heard what was happening we went straight to the area - we knew who we were looking for and what we were going towards but we knew that if he wasn't stopped he could hurt someone else," he said.
PC Wright said: "I didn't expect this - it's taken me completely by surprise. I am really humbled and honoured to receive it."
West Yorkshire Police Chief Constable Dee Collins said: "I am delighted that the brave and heroic actions of Bernard Kenny, PCs Craig Nicholls and Jonathan Wright have been recognised in this way.
"They all showed tremendous courage putting other people's safety ahead of their own."
The man who tried to stop a right-wing extremist from murdering MP Jo Cox has been awarded the George Medal in the Queen's Birthday Honours List.