Missouri Digital Heritage
http://www.sos.mo.gov/mdh/ They have both government records, state and local, and family and church records as they are provided to them. Adding records every day. On the off chance someone has contributed something, say a diary by a soldier in the unit your man was in in MO, it should be searched. If you live in MO and have historical family papers or artifacts, consider donating them for public use to this wonderful archive.
Maryland land records online are an incredible resource, almost all deeds and slave sales and emancipations filed with the county recorder of deeds (this practice varied by county) online free. If you are researching a Maryland resident who owned property, you are very lucky to have this.
https://mdlandrec.net/main/
The above archive is part of the Maryland State Archives, among the very best I've seen with more and more digitization daily. msa.maryland.gov Also good for the Colonial and Revolutionary War periods. What is not yet online is available on request at their facility in Annapolis.
Some counties in West Virginia have also digitized land records. See for example documents.jeffersoncountywv.org
The indexing system takes a little trial and error (for me anyhow) but the records are there.
Also, familysearch.org may have copies of your subject's Will and estate proceedings, testate or intestate, online. Familysearch.com's progress in this regard varies with location and they have both searchable images and many as yet unindexed originals uploaded for browsing. If you can find the Index to the court records in the original record book or in an original index book, you can find the volume and page number of your subject's documents even in the unindexed files. Date of death or approximate date of death will spare you a lot of browsing time.