Plant big shady trees and grass around the coop. When the trees get big enough they'll provide shade which will keep the grass cool. Half our lawn is shaded by a massive privet tree, the other half isn't. The one half is MUCH colder than the other. It's not immediate help though, but in the long run it will help. Also, I have misteres set up which help, but that will add to the humidity. I live in California, so I'm set up for dry heat, not humidity and heat. Soaking them with the hose helps, but be sure to wet them to the fluff. Fans, lots of shade, shaded mud, that might help.
Be sure to keep their water cold! Chickens will drink frozen water, but if it's too hot they won't touch it, even if they're dehydrated.
Be sure to keep their water cold! Chickens will drink frozen water, but if it's too hot they won't touch it, even if they're dehydrated.