The Disneyland Resort sits five miles southwest of Placentia in Anaheim — close enough that the fireworks are audible from many Placentia neighbourhoods on summer nights. The reason a lot of visitors to Placentia are here at all is to use the city as a quieter, cheaper base for a Disneyland trip.
From central Placentia it is a 15-minute drive to the parks in light traffic and double that during peak commuter hours. There are buses, ride-share is straightforward, and several Placentia hotels run shuttles. Plan the actual Disneyland day in Disneyland's own pages — this is just the reminder that it is close.