The open-air markets in Chicago run, in general, from May to end of October in specific neighborhoods. The Green City Market is the main organic option but they all sell only sustainably-grown vegetables and fruits as well as seasonal products. The price level is, as a result, rather high. There is no special etiquette, but bargaining is not welcome.
The Green City Market (http://chicagogreencitymarket.org/) promotes local and sustainable farmers. You will find there only organic products. It is an outdoor market through October 31st, Wednesdays & Saturdays from 7:00 am to 1:00 pm. The outdoor market is located at South end of Lincoln Park between Clark and Stockton. From November, there is an indoor market at the Peggy Notabaert Museum on the same days from 8:00 am to 1:00 pm.
61st Street Farmers Market: Every Saturday from mid-May to Oct 31, from 9:00 am to 2:00 pm at 61st between Dorchester and Blackstone Avenues (6100 S. Blackstone Chicago, IL 6063). Admission is free.
Andersonville Farmers Market: The market runs weekly (every Wednesday), from June to September. Weather permitting, it may be extended over the fall (see the website for more information about the extended dates). You will find sustainable and organic produce as well as honey, cheese, and wine. There are also live musicians, family-focused activities, and chef demonstrations.
Bronzeville Community Market http://www.qcdc.org/. This market runs weekly every Saturday from May to October; featuring local farmers, artisans, and retailers. It is held at 4400 S. Cottage Grove from 8:00 am to 1:00 pm with live entertainment.
Chicago’s Downtown Farmstand, located at 66 East Randolph Street, is held on Mondays and Fridays from 11 am to 7 pm and Saturdays from 11 am – 4 pm. You will find there in season vegetables and fruits, all of them sustainably-grown.
City Farm Heirloom Tomato Stand runs from Monday to Friday, from 3 to 6 pm; and on Saturday, from 10 am to 1 pm. It is located on 1204 N. Clybourn Ave. Chicago, IL 60610.
Edgewater Green Market runs from July to end of October, every Saturdays, from 7 am to 1 pm at the crossing of Broadway & Norwood.
Independence Park Farmers Market is located at South side of Irving Park between Springfield and Hamlin. It runs from June to October on every other Sundays from 9 am to 1 pm.
Logan Square Farmers Market (http://www.logansquarefarmersmarket.org) runs from June to end of October, every Sundays from 10 am to 3 pm on Logan Square (3107 W. Logan Blvd.).
Pilsen Community Market http://www.pilsencommunitymarket.org/ This market runs every Sunday from mid of June to end of September from 9 am to 2 pm. It is located on Chicago Community Bank Parking Lot (1800 S. Halsted. Chicago, IL 60608).
Portage Park Farmers Market http://www.friendsofportagepark.org/market.html#FMkt. This market runs every Sunday from end of June to beginning of October from 10 pm to 2 pm. It is located on corner of Berteau and Long (4100 N. Long, Chicago, IL 60641).
Rowan Trees runs every Saturday and Sunday from 8 am to 4 pm from May to end of October at Garden Society and 4-H Club, Englewood Ave. and Normal Boulevard.
See also the Chicago French Market under Specialized Groceries.