I'm still searching for specifics, but as near as I can determine at the moment, the Illinois Glass Company in Detroit appears to only have been in operation (at 220 Jefferson Ave.) for two years in 1902 and 1903.
If the Illinois Glass Company was in operation in Detroit for only two years (1902-1903) it seems mighty coincidental to me they were located there at about the same time that James Vernor might have started bottling his ginger ale. Especially when you take into account they were only a few blocks away from each other.
How come only 2 short years. Keiths Siphons don't have that Illinois makers mark. I guess the good thing is that if we could find a Vernor's with that mark we could pin point it to 1902-3. Unless made outside of Detroit. No Coincedence, Lots of other soda & brewers were in the same area. LEON.
1. The manager's full name was Kenzie G. Smith
2. The company was located there at least as early as 1902 and as late as 1909
3. For a number of years it was called Illinois Glass Company & U.S. Bottlers Supply
Based on some other tid-bits of information, the company appears to have been a distributor, supplier, warehouse and not a factory. And even if there are pre 1929 Vernor's bottles with the Illinois Glass mark <I> it might be hard to precisely date them and determine their exact place of origin. But it might be worth looking into if any Vernor's bottles have the <I> mark, especially the extract bottles.
<I>
Illinois Glass Company. Alton, Illinois (1873-1929). This mark was used from approximately 1895-1915.
Putting the siphon bottle theory aside and returning to your basic soda pop bottle, this looks like its going to be the best and earliest I'm going to come up with ...
July 1902
Everything preceding this appears to be related to siphon and/or extract bottles!