@aggro_jo
" Being local, I can say your best bet is stay on the east side and then cross the Miss on the Alton Ferry."
surely you mean the Grafton Ferry? There is no ferry in Alton. You can take the Alton Bridge, and worm your way over to St. Charles, but that way requires some stints on 94, which I do NOT advise- narrow, no shoulder, fast traffic, limited sight lines. YMMV...

@gus:
The map shows the route through St. Louis to St. Charles- I have ridden this route several times with no problems. There may be shorter routes, that others could advise on, but this one is scenic and enjoyable. It'll dump you out at the Casino in St. Charles, basically on the Katy Trailhead.