Around 30 traveller caravans have moved onto land at Penwortham Holme Recreation Site.
Police were called by a member of public at 8pm on Monday, saying a group of travellers were trying to get in through the main gates off Liverpool Road.
When officers arrived on the site, the travellers moved on, but then were reported to have returned at 9pm.
This morning a large encampment could be seen on the playing fields.
Officers from South Ribble Council have been sent to conduct a site survey and check on welfare needs.
It is not known if they are the same families who had pitched their caravans in Moor Park, Preston, on Thursday.