The park, while located within Joliet city limits, has a Plainfield address and is maintained by the Plainfield Park District.
Joliet police said officers responded to Cumberland Park on Tuesday at about 11 p.m. for a report of mulch and playground equipment on fire. The Joliet Fire Department then came and extinguished the blaze.
Police estimated the fire caused more than $20,000 in damage. No injuries were reported.
The Plainfield Park District said in a Facebook post that the swing set and the rest of the park will remain open, but the playground structure is closed for an indefinite period of time. They are asking anyone with information to contact Joliet police.
Police said the cause of the fire has not yet been determined.