According to West Sussex County Council, there are ten caravans and motorhomes parked at Hamble Road in Sompting and another eight caravans based at Goring Gap.
The council said the travellers at both sites have been served with a notice requiring them to vacate the land.
"Should they fail to do so, court proceedings will commence,” a spokesperson added.
“We will continue to monitor the site[s] together with Sussex Police.”
Sussex Police said it is aware of the unauthorised encampment on the Hamble Road recreation ground and officers ‘are in conversation with the local council’.
The police force confirmed that the travellers based at Kingston Broadway in Shoreham-by-Sea had been moved on, after they were served with a notice requiring them to vacate the land.
This comes after dozens of caravans move onto private land in Angmering and East Preston.