Many Missouri researchers may be aware of the great resource the six volume set of the Missouri History Encyclopedia. Published 1901, the set is organized alphabetically with vol 1 (A-Ci), vol 2 (Ci-Ga), vol 3 (Ga-La), vol 4 (La-Nu), vol 5 (O-Sl), and vol 6 (Sm-Z).
There are a various websites that have the books digitized and I find it useful to go between the sources for maximum search options, especially with older books that do not have an index. Ancestry has it here. Ancestry is focused on people so if you know a specific name you can look it up with the search function. That said, I don't find it easy to browse on Ancestry, instead I use Google books or Archive.org. Google is great because you can type in any search query and may find page numbers for town, maps or other details you seek. This set is on Google Books, but if you do not find a book there, you can go to Archive.com and download the full book via pdf, save it to your own computer and go directly to the pages you seek.
If you want a hard copy of one or all of these volumes reprints can be purchased on Amazon.com.