Coun Pauline Markham, who represents Labour on the Darfield ward of Barnsley Council, was walking her dog at RSPB Old Moor/Broomhill Park nature reserve near Wombwell when the incident happened on Thursday afternoon.
According to her ward colleague Coun Kevin Osborne, Coun Markham was approached by a man who made remarks about her political work before punching her in the face, knocking her to the ground.
She was discovered by a passer-by 'dazed and in pain' and taken to hospital, where she was diagnosed with concussion. She is now recovering at home.
Coun Markham has been a councillor since 2010 and has also served a term as mayor of Barnsley. Originally from Wath-upon-Dearne, she has lived in Darfield with her husband Larry for over 20 years and has campaigned against loneliness and social isolation.
The man who attacked her was also walking a dog, described as a Staffy-type breed, and was white, aged 30-40, of a stocky build and wearing a black hoody and blue jeans. He left the park via the Old Moor Tavern entrance at around 2.30pm.
Coun Osborne said: "Pauline was assaulted by a stranger who attacked her because she is a councillor. Pauline will recover; she's made of Barnsley. Her attacker will always be a little coward."
Acting Inspector Kevin Jenkins, from South Yorkshire Police’s Hoyland Neighbourhood Policing Team who are overseeing the investigation, said: “This is an awful incident which has left a woman needing hospital treatment and will not be tolerated."
Officers are now seeking to identify the man involved. He is described as white, about 5'7, of medium build and aged in his early 40s. He spoke with a local accent and was wearing a black hoody and jeans. He had a brown Staffordshire bull terrier with him.
If anyone was in the area at the time and saw or heard anything suspicious, or has CCTV footage which may have captured the incident occurring or where the offender left in the direction of, they are asked to call 101, quoting incident 432 of 18 November.
A/Insp. Jenkins added: “We are now acting quickly to try and find the man involved. If you have any information which can help the investigation, no matter how insignificant you think it may be, please get in contact and help us to find him.”