My last ant invasion was going on for several days when I'd finally had it!
My ant problem was on the kitchen counter, so I pulled all the appliances off and sprayed the entire area with Glass Plus, to kill whatever ants were there presently and also to be sure (once again!) that there was nothing there to attract them, like crumbs, spills, etc.
I then sprinkled about 2 tsp of quick cooking oats into a small mound on the back corner of the counter, where it meets the stove. This seemed to be where they were coming in: the back wall behind where the counter meets the stove. (Apparently they take the oats back to the nest, the ants feast on them and then die because they can't eat foods that expand.). Place your oats or grits as close as possible to where you think they're coming in from. You don't want to attract them so they'll stay around! You want them to grab some food and take it back to the nest immediately.
Then, I took a bottle of cinnamon (the dollar store kind -- not an expensive brand) and sprinkled it all across the back of the counter (stopped at the oatmeal) and then sprinkled it down into the crack between the counter and stove. Apparently, ants don't like cinnamon and they won't cross a line of cinnamon. I have no idea why they won't, but I made sure to sprinkle an unbroken line (until I got to the oatmeal).
After doing all of the above, place your appliances back where they were (check for any ants on said appliances first). My counter is small, so the appliances cover the cinnamon line and the kitchen smells nice!
Right after I completed the above process, there were a couple hangers on, but I shot them with Glass Plus and wiped them up. I'm assuming they were already "over the line" somewhere I didn't see them or they rode over on my appliances.
It's now been well over 24 hours and I haven't seen one ant on the counter or on the side of the stove. I'm leaving all as is for a few days and then I'll clean up the cinnamon and oats.
Hope this works for you!