Cook County has a ban on high cap magazines:
Effective November 14, 2006, a Cook County gun ban Ordinance criminalizes the otherwise lawful possession of many common firearms and large capacity magazines. The law provides for imprisonment up to 6 months, fines, and confiscation and destruction of the enumerated weapons. Owners of such firearms or large capacity magazines have until February 12, 2007 to either remove the affected guns and remove any large capacity magazines from Cook County or surrender them to the police for destruction.
What firearms and magazines are affected by this county wide ban? Over 60 firearms are specifically listed as being illegal, including the deer rifle popular in many Midwest states, the SKS with a detachable magazine. Popular self defense weapons like the Mossberg 500 pump, and popular target shooting semiautomatic AR-15 are also illegal.
In addition, all magazines that can hold more than 10 shells are banned.
The Ordinance specifically bans any semiautomatic shotgun that has a fixed magazine with a capacity in excess of five rounds. Since shotgun shell rounds can be obtained in sizes as short as 2 inches, the ordinance can be construed to ban all common semiautomatic shotguns.
In addition to banning over 60 enumerated firearms, the Ordinance defines certain banned firearms with catch-all definitions. One such carefully worded definition bans any semiautomatic rifle that need not have, but has the ability to accept a large capacity magazine and has,
"A shroud attached to the barrel, or that partially or completely encircles the barrel, allowing the bearer to hold the firearm with the non-trigger hand without being burned, but excluding a slide that encloses the barrel,"
Rest of article at
http://www.isra.org/legislation/cook_county_awb.shtml