I am a newbie and want to prevent this. Were your chickens out of the coop? Was the coop opened by the coon, or a hole dug? Did this happen in the day or night? This info will help me building my coop. I want an open bottom run but if the coons dug under I will take my dad's advice and make it a screened bottom. I am so sorry this happened to you. I have a two year old and four year old and while they need to learn about these kinds of things I'd like to prevent this from happening if I can.
One of the best pieces of advice I saw here was to view a raccoon as a very persistent 5 years old child- if a five year old could get in, so could a raccoon. They can open latches, unwrap tie wires, pull things apart.
Use hardware cloth (the welded square wire mesh) not chicken wire, don't allow any gaps bigger than 2" x 2" (and try not to even allow that size anywhere), and if the bottom is open, dig down around the outside and bury the hardware cloth, also put a cloth apron 2 feet around the run- but animals still may be able to dig under.
Look in the coop building section here for more ideas. A lot of people use electric fencing and hav-a-hart traps.