Hi Amber!
I'm in Phoenix so we have similar "issues" with heat.
Here are the things I've done:
--Make sure there's lots of airflow
--Make sure there's shade and lots of it in the hot season(s) - this could be a tree (like a mulberry which would drop fruit into the hen yard) or vines, or shade cloth or a combination of all of the above.
--In the summer time, I do have a mister system and a fan going. However, I find that this wastes water BUT I want my hens to be comfy. So during the very hottest time of the year, I let them roam the backyard. They will do their foraging early in the morning and then find the coolest spot for themselves for the heat of the day. Usually this is under my densely planted urban orchard that's planted in a swale. And sometimes it's on the back patio because they can look in at me in the office through the back door. I put frozen 2 litre bottles of water out on the patio for them. I prop the bottom up on a brick and open the top. The water slowly melts throughout the day. They enjoy drinking the cold water as well as standing (and pooping) in the puddles that form.
--This year, I may try building this tiny swamp cooler for them