The laws in Illinois--contrary to what some people believe--are pretty specific and very much in line with the rest of the country, I think.
If you're only using the Tempest for hunting and fishing, no one will really stop you, even in Chicago, except to ask to see it and find out how you like it.
In theory, it's always illegal, but in practice, you can easily get by with an even larger blade--just don't walk around with it in public. You can certainly wear it while hunting or fishing or camping or even working on your landscaping at home.
Movie theaters, shopping malls, public transportation hubs--these would be bad places.
I would not give a similar knife to a minor, however: all it takes is a friend of his to tell his mom "but his parents let him carry a Buck Tempest," and well--he'll lose the knife at the least, and possibly get in trouble at school.