The responses so far as to when to leave Chicago have suggested a range, September 1 to October 15 is correct. In making the decision an important factor is whether your air draft allows you to go through the Chicago River (downtown route). If this is the case your date for leaving Chicago can be extended because you can avoid almost all of the weather on Lake Michigan by entering the Chicago River which is immediately between Monroe Harbor and the DuSable Marina. If you can't clear the bridges on the Chicago River than you have a 12 mile trip on Lake Michigan. In October this could mean waits of several days for calm weather to make the trip. Today is September 22 and the weather the last couple of days has not been good for such a trip. I went by the harbors on Saturday and there were a thousand boats still in the water. All of these boats will have to make either trip. When we had our Krogen in Burnham Harbor we waited until mid-October and then took off work to haul the boat on the first good day. Once you leave Lake Michigan for the rivers the fall weather is no longer a factor. A warning on Monroe Harbor. The mooring field is half empty at this time of year. Avoid a mooring ball near the entrance to the harbor (directly center of the harbor). The wave action in late September and October rolls these boats uncomfortably. Marty Bay Pelican KK42