There's Bernardi's, which the locals love. They have an ok pork tenderloin sandwich.
DeLong's has a nice outdoor sitting area on the square. The lunches are good, sweet potato fries are good. There's a relatively new restaurant called Lydia's Cup. I went once, and haven't gone back.
If the Apple Tree is open, they have homemade pies and homey food. Along the square, I like Apple Tree & DeLong's the best.
There's also a Monical's pizza on the outskirts of town, as well as La Mex and Cafe Fontana.
If you feel like a little bit of a drive on from Pontiac, Lost in Time in Fairbury is good, with all desserts made in-house at their bakery.
Enjoy the murals, stop in at the "made in Illinois" store, the art gallery, and the cute antique store, all on the square.