Fire crews rushed to the park after a viewing platform overlooking the duck pond was set alight at 4.20pm yesterday (June 1).
An initial investigation suggests that an accelerant had been poured onto an interpretation board before spreading across wooden decking.
Thick, black smoke could been seen billowing above the park from miles around.
The scorched viewing platform, willow screening and interpretation boards had been funded by local volunteer group 'The Friends of Walton Park'.
A wildlife shelter and a birdhouse, which had been home to a nest of blue tits, has also been destroyed.
No injuries have been reported.
A fire service spokesman said: "One fire engine from Chorley was called at 4.20pm and they used one hose reel to extinguish the fire."
Lancashire Police has been approached for comment.
Earlier that day, Lancashire Fire and Rescue Service said it had reported video footage of youths deliberately starting fires in Worden Park, Leyland.
The footage is being investigated by police.