Is it allowed to camp along palouse river banks in Washington or do you really need to find a campsite. We're just thinking of random trip and just camp for a night.

The river has few areas with road access. The banks and river itself are under federal jurisdiction (army corps of engineers) there are places where camping would be possible though not necessarily "legal" I doubt if you would be hassled and worst likely case an officer might make you leave. Campsite cleanliness would likely play a role in either govt or private property owners reaction.

On site camping, on the river, depends if you are thinking above the water fall maybe, but the ranger did tell me that he has seen poisons snakes on top of falls. You should stay by the park enterance the rangers can help you. Happy trails. ( By the way someone kayak off the fall a couple years ago.). :=)

The park has campsites but donot know about anyplace near there to camp along river.

There are campsites in the park but not along the river

I am not sure about it. You can,check the WA states park website.

You can check Washington state park regs. Online