One snake per tank. Housing corn snakes together is NOT a good idea. There's plenty of reading to do around the forum that'll rehash the MANY reasons why many times over for you, though I'll mention one of the more devastating possibilities here:
Corn snakes DO eat each other. Hatchlings are the biggest risk in this. It is most definitely possible for one hatchling to eat its cagemate, even if they're exactly the same size.
Like hypnoctopus pointed out, corn snake hatchlings don't need to be housed in big tanks from the start. You can get a couple 10 gallons or even a couple 6 or 15 quart Sterilite tubs (and binder clips!) and they'll be happy in that size for quite awhile--up to a year or so, depending on how quickly they grow.
Regardless of what you choose to do, don't forget about quarantine. Any new snakes should be put under quarantine for at least a few months before being allowed anywhere near your other snake(s). This means putting the new snakes as far from the established one as possible (in a separate room, if possible), practicing strict hygiene before and after handling any snakes, completely separate sets of tools... Basically, you want to avoid any cross contamination at all, just in case one of your snakes is carrying some contagious disease/illness/parasite that could be spread to one of the others.