How do I get rid of huge quantities of ants building nests in my yard?

Use your feet. Step by step by step. It's slow but certain

pouring boiling water on the hills everytime you see the hills come back worked for me.

A few decades ago 'Organic Gardening' magazine posted a sure fire ant bait: 2 cups water, 1 tsp boric acid powder, 6 Tbsp sugar. Boric acid powder is available and inexpensive in the pharmacy of my local Walmart. Make the mix, soak a few cotton balls and make dispensers out of old margarine containers (or whatever) by making slits in the top, placing soaked balls inside and covering with lid. Place outside. I usually dribble a bit outside the container to begin quicker attraction. The slits permit ants in, critters out. This is a weaker solution than some ant baits which is why it is effective. They carry bait to the nest and within 3 or 4 weeks the nest is dead. No, it isn't instant but it truly works. It will even kill fire ant nests if you are patient.

Ant powder on ant mounds, I had loads of ants now majority all gone.

I had a mix of black and red ants

boiling water on the nests

I used borax on several huge ant hills in my yard. That was several years ago and the ants never came back. I am currently working on an ant trail and hill at the back of my property. Good luck.