I stopped by Rod's corn on Monday the 12th to find a little bit of freeze damage. This can be a bit disconcerting to look at, but is actually completely harmless at this stage of growth.
In this picture I have pointed out the growing point of the plant. You can see that it is still quite a ways under the surface (anything that is white is below ground.) It won't emerge until around the V5-V6 stage (5-6 collared leaves(this plant is at V1.)) Until then it can freeze or hail all it wants without doing any significant damage to the final yield. (Some studies have hinted at a yield boost after a hail at the V2 stage!)