West Sussex County Council has confirmed the date the travellers in Horsham Park must leave.
The group, which moved into the park from Victory Recreation Ground, has been issued a notice to vacate for tomorrow (Tuesday, August 13).
The council said the group must leave or court action for an eviction order will begin.
A West Sussex County Council spokesman said: “This morning we attended the site to carry out health welfare checks on the group of travellers.
“A notice to vacate has also been served which cannot be acted upon until tomorrow.
“If the group remain tomorrow, steps will be taken to commence court proceedings to seek an order for the group to leave.”
Sussex Police has been patrolling the park, Horsham District Council said earlier today.