Here an easy non chemical method. We don't have fire ants in the area in Michigan I live, so I have no personal experience.
Diatomaceous Earth, check out suggestions for "Diatomaceous Earth" &"Fire Ants on Pinterest.com
I spread out the ant hill and drowned the area with Raid ant killer.
Amdro is the only product guaranteed to get rid of fire ants. And it works the first time.