Guess I am the only one who would take a ladder and a pry bar, climb up and remove one or two of the boards to create a temporary opening so the hawk can fly out.

How big is it?
It would work best if it could see movement of the prey to trigger it to go after it since they hunt visually for the most part (but they can also smell and hear). As I understand, they are principally bird hunters, so if only some other birds would fly in and out it could hunt them and then get out, or alternatively, pay attention enough to learn the way out...
I don't know if you can find "feeder birds" at your pet store, but if you could, you could release some in the barn to both feed it and show it the way out...
Can you get up high in your barn? If you can, perhaps you could create some stress by visiting the lofty areas and drive the hawk down and out.
You could install a hawk window, and maybe by the time you were done it wouldn't need it anymore, but the next one might appreciate it...

I originally thought about cutting a hole or something... LOL

yes!
--I guess I'm visualizing my old 'barn'--which was a Quonset, and pretty much all roof--I wouldn't have wanted to put a hole in it. But if you have walls that you can open a portion of and let it out, that could work

Let's see some photos of the outside of the barn and maybe we can think of more ideas.

You might be able to call your local wildlife rehab center or aviary etc. (if you have one) and they could help/give suggestions....

Maybe you could hang a bird feeder or two in the doorway, chum some birds around, and it will figure out the doorway.
I almost hate to suggest chumming birds into or near your barn, but...just temporarily... and it might work better than a rodent in a cage

The barn is all steel and about 30' high inside. I guess if I set a ladder up in the back of one of the trucks it might reach, but I am not keen to destroy the roof/walls. I already tried to chase it out with a high pressure hose. He did not leave, but he's nice and clean. Sparrows normally fly through the barn all the time, however with a hawk in residence, the sparrows have been absent.

The wildlife people suggested the mouse in a cage approach.

Poor confused little guy. I sure hope you can get him out.

Thanks, me too!

Porkpal, I think you said it was a red shouldered hawk?
We have resident red shouldered hawks here & have numerous times observed them eating earthworms, yes earthworms, Sucking them up like mad! How about a mouse in a cage & a box of earthworms beside it? Double the attraction. I imagine you must have doves or quail around ~~~ triple the attraction by throwing some seed on the ground to bring them into the yard outside the door....... Kind of the "throw everything you've got at it" method.

I believe it is a Coopers hawk. I usually see them hunting meadow mice, so pursuing the mouse suggestion is my next project.

Perhaps the bird is just hanging out for a few days because he or she thought it was a good place to hunt for mice. Or maybe pigeons? do you have any Rock doves or Mourning doves hanging out in the barn?

Anyway, you are not alone. I found a blogger who had a hawk visiting in their barn for a few days. Eventually it flew out the door.
http://thekitchensgarden.com/2...

(Note to self: when I become a famous designer of barns, remember to include a remote controlled 'hawk escape window' when planning the design.)

Maybe set a light outside that shines partly into the barn through the open door. If it is the only spot of light at night, it might attract him.

That blogger that greene mentioned said that her hawk flew out overnight. Do you leave the doors open at night?

The hawk is free! He left sometime between 5:30 and 7:30 this morning. I have my barn back!


(No chickens, mice, or hawks were harmed in this endeavor.)

This was better than a cat-stuck-in-tree story. I am so very glad it has a happy ending.

Smiles,
Lyn

A happy ending. You can't beat happy endings.

And the barn was not harmed either. Good thing you didn't listen to me!