I'm in the midwest, Northern Illinois area. Put your plants out the last week of May and you'll be A-Ok. Cornfields are popular spots around these parts, but can be dangerous. I've heard tails of people getting shotguns held to their heads after stumbling on another's patch in a cornfield. Along creek banks are good, but be sure you are in a zero-traffic area. Also, be sure the ground you plant on isn't prone to flooding. If you choose to do your thing in a cornfields, start indoors and put your seedlings out after the 2nd week of June when the final application of chemicals is put down on the corn. Also, remove two stalks of corn for every lady you plant. This will ensure they receive enough light and do not have to compete too strongly with the corn. Wherever you decide to plant, be sure to keep your numbers small and use your surroundings as natural camouflage.
Good luck!