Twenty-year-old Penny Hill was found unconscious with severe head and face injuries near Coolah on July 8, 1991.

She died in hospital nearly two weeks later.

READ ALSO:

- Water infrastructure spend to tighten council's purse strings

- Dozens of cattle seized, tip searched as police raid two farms

- City solar farm could power more than 6700 homes

Police said detectives are re-investigating Ms Hill's murder and a $1 million NSW government reward will be announced in acknowledgement of the 28-year anniversary.

The reward will be offered for information leading to the conviction of those responsible for Ms Hill's murder.

Australian Associated Press