They have maps from before the US was founded to current. One interesting set of maps are the panoramic maps of several cities made right after the Civil War. They look like someone went up in a ballon and sketched the layout of the town. Some of these on file are Mexico, Macon, Palmyra, Carthage, St Louis, Kansas City - there are 40 or so of them.
(I found the house my ggg grandfather built in Hermann, MO in the 1840's)
To easily find those, In the SEARCH bar, click on the drop-down for MAPS and then enter PANORAMIC MISSOURI to the right. A listing will appear. (They have these types of maps for all over the country.)
Or just click on MAPS and enter MISSOURI and several maps will come up, many from the Civil War era.
You might have to download a special viewer program (like IrfanView) which is free and will view almost any type of image file.