@Rod - I pride myself on knowing Illinois, I had to look up Secor. That's not terribly far from Peoria. Far enough south that these days I would say you are more zone 6 than zone 5, unless you are in wide open prairie or farm fields.
I have not been able to successfully winter trident seedlings outdoors without protection at my home, near Lake Michigan, right at the IL-WI border. Tridents are not reliably hardy this far north. Now there may be some variation due to source of seed, some southern China or Taiwan sourced seed might be less cold tolerant than seed sourced from more northern areas of Japan, Korea, and more northern areas or China.
There is also the possibility that someone was looking at Acer ginnala thinking they were looking at a trident, Acer ginnala is very, very winter hardy, and to some degree superficially resembles a trident maple, until you take a close look. I highly recommend the Amur maple, Acer ginnala for anyone living in zone 6 thru zone 4, as they can be wintered with little or no extra protection. I've heard they can be wintered in zone 3 with only a little extra protection. I winter my Acer ginnala simply by setting its pot on the ground for the winter. That's it.
Tridents are really a tree for zone 6b and warmer. Acer ginnala is the one to use for 6a thru 3b.