I.D. the Ant
Start by identifying the type of ant in your house so you can find out its nesting habits and have a better idea of where they're living (they may be nesting outdoors). Take a close-up photo of the ant and send it to your local university extension service (enter your state's name and “university extension service” into any online search engine). The extension service will tell you the type of ant you're dealing with and where it nests. They may give you fact sheets about the ant species and maybe even some advice on getting rid of that particular ant species.
Keep it Clean to Deter Ants
A clean house is your first defense against ants. Sweep up food crumbs, wipe up spills, take out the garbage and don't leave dirty dishes sitting around the house. This takes away the ants' food source. Spray vinegar mixed with water around bowls of pet food to keep ants from feasting there.