I rode the KATY with my two young sons in July 2010.
July/August are likely to be hot and that is an understatement. We had 105F+ and the trail runs right next to the river where it is very humid. Mosquitoes will also reach horror movie concentrations - swarms that would cover any exposed flesh.
The trip planning website (
www.bikekatytrail.com) has everything you need to know but don't expect to find lots of eating places open. Some are only open a few days a week and a few places were long abandoned.
The only indoor night we had was at Doug Rendleman's place near Bluffton. He is an easy going character, fed us well, told us stories. If you are laid back it's a great place to stay but you need reservations.
Everywhere else we camped - very relaxed, just throw a tent up on the local ballfield (we even watched some softball). Don't expect people to go out of their way to meet you but everyone is pleasant and helpful. Don't expect any services after 9:00 PM.
Hermann is popular with people who like charm, wine, antiques, etc. A little too fancy for our tastes. I'm sure you will find lots of places to stay. Rocheport also caters a lot to bike tourists. N. Jeff City is a ghost town since an earlier flood. You will need to ride into Jeff City proper to get any services.
The ride out as far as Rocheport is stunning (by Missouri standards). They did a great job documenting the Lewis & Clark expedition and you will ride with Bluffs on one side and the wide river on the other. 2010 was a flood year and we had one detour and one spot where we were in over our chainstays.
After Rocheport you hit some open farmland until Booneville. Not much to see but not a long run either. From Booneville south you are on elevated rail bed and in timber. Very nice.
Trail surface is pretty well maintained - one of the best I've seen. You won't need fat tires but very narrow tires could be a problem. Mine were 28s and no problem. Prepare for flats though - there are thorns and other hazards.
If you have any other specific questions let me know. We had a great time in spite of the bugs and heat.
If I were to do it again I would bring along a copy of Lewis & Clark's journal and read about the trip as we went along. It makes your journey seem pretty comfortable by comparison.