I have a 2003 Ion. In Nov. 2008, I couldn’t turn off the ignition. Many friends tried to help, but no one could turn it off. Finally, we disconnected the battery and I had it towed to a mechanic. They changed the ignition switch and celluloid. Worked fine until last Friday night on my way home - couldn’t turn it off. Had to drive back ti the mechanic, but they were closing and can’t work on it til Monday. Any idea as to why this is happening. I had another car for 10 years and never had to change the ignition switch.
This vehicle has a couple of recalls for ignition switch modules. Looks like they still have not completely fixed the problem. Saturn is now defunct so you might want to stash an extra module away if you plan on keeping the Ion for a few more years.
“Celluloid is the name of a class of compounds created from nitrocellulose and camphor, plus dyes and other agents. Generally regarded to be the first thermoplastic, it was first created as Parkesine in 1862  and as Xylonite in 1869 before being registered as Celluloid in 1870. Celluloid is easily molded and shaped, and it was first widely used as an ivory replacement. Celluloid is highly flammable and also easily decomposes, and is no longer widely used. Its most common uses today are in table tennis balls and guitar picks.”
The solenoid has nothing to do with turning the engine off. It’s only involved in the starting process. Is it possible they saw you coming? Did they give you the old ignition switch? Not a sermon, just a thought. Per Missileman, ask them to look up the TSB’s on the ignition system (Technical Service Bulletins).