Is it true that farmers grow corn by planting cow corn on the out side and sweet corn on the inside of the field so that people don't take the sweet corn?

Actually no.. quite on the contrary if any. If the farmer grows both cow corn and sweet corn, the way we did it was the sweet corn on the outside 3 or 4 or however many rows, and the cow corn on the inside. It made it easier to pick, and you didn't ruin any cow corn when you tried to harvest it, because the outside was sweet corn which had already been picked.

Additional Info.

While it is very occasionally done, as both the answer above and one of the discussion points mention, it is only done in either way (outside or inside the field) on a very small portion of the field -- for the farm family's convenience. If you want high quality sweet corn, it must be planted in a location isolated from field (cow) corn, or any other type of corn, because the other corn's pollen will make the sweet corn kernels go "starchy". The best sweet corn (and what you buy in the can or frozen) is grown in a field all by itself for this reason.