I don't know what part of the Milwaukee area you are in, but as far as public land nearby goes, you should be prepared to deal with a lot of other hunters. 99% of the guys out there are courteous and won't crowd you, but then there is always that other 1%.
To the north of Milwaukee there aren't many decent areas open to the public, there are more to the west and northwest.
The Horicon marsh is arguably one of the best waterfowling spots in the country and is a fairly short drive. The state wildlife area up there is open to waterfowl hunting, but you need a special permit to hunt geese in that zone.