Permit
Waimea Canyon State Park Permit
If you plan to visit Waimea Canyon State Park (and Koke’e State Park) for the day, you do not currently need a permit.
If you plan to camp overnight in Koke’e State park, you do need a permit, which can be obtained here.
If you are not a resident of Hawaii, you do need to pay an entrance fee (and parking fee) for day use of the state parks.