The Illinois Senate has passed a law "decriminalizing" small amounts of cannabis, according to a Chicago Tribune and WGN-TV report. The bill still needs more revision and work before being sent up to Governor Rauner to become law, but it's a significant step, with Illinois possibly joining 17 other states that do not treat small amounts of marijuana possession as a crime.
However, that's not the same as being legal. Under the proposed law, possession of small amounts of cannabis will still be a petty offense subject to a citation and a fine. Think traffic ticket.
While the debate about legalization (or at least decriminalization) of cannabis still rages, there's very little debate about another proposal in the same proposed law - the elimination of the presence of non-intoxicating metabolite left over after cannabis consumption as presumptive evidence of DUI based on marijuana. As of now, the presence of metabolite resulting from cannabis use in urine, even though not indicative of actual impairment due to marijuana use, can for the basis for prosecution of a DUI under what is called a per se violation. Most of the rest of the country has moved away from such a misguided and unscientific approach long ago.