I'm not a lawyer either, but my understanding is that is legal to open carry a large knife in Illinois.

Once you knife exceeds 3", you are "considered armed with a dangerous weapon", but this in itself is not a crime.

If you do commit a crime with a knife over 3" the penalties increase.

Having said that, I think if you tried to open carry a machette, would probable be charged with disorderly conduct.

Also, many of the small cities have ther own laws, so you need to be careful.