9th Regiment, Missouri Infantry (Union)
The book "Compendium of the War of the Rebellion" by Frederick H. Dyer contains no history for this unit. 
Companies in this Regiment with the Counties of Origin
Men often enlisted in a company recruited in the counties where they lived though not always. After many battles,companies might be combined because so many men were killed or wounded. However if you are unsure which company your ancestor was in, try the company recruited in his county first.
Company D - Captain Jerry D. Hill, Captain William R. Renfro - enrolled in Marine, Madison County
The information about the companies and counties is from Kenneth E. Weant's book, Civil War Records, Missouri Volunteer Infantry, Volume 2, Three Year Volunteer Regiments 4-10, (Arlington, Texas: K.E. Weant, c2011), pages 93-94. FHL 977.8 M2wkv v. 2
- Beginning United States Civil War Research gives steps for finding information about a Civil War soldier or sailor. It covers the major records that should be used. Additional records are described in 'Missouri in the Civil War' and 'United States Civil War, 1861 to 1865' (see below).
- National Park Service, The Civil War Soldiers and Sailors System, is searchable by soldier's name and state. It contains basic facts about soldiers on both sides of the Civil War, a list of regiments, descriptions of significant battles, sources of the information, and suggestions for where to find additional information.
- Missouri in the Civil War describes many Confederate and Union sources, specifically for Missouri, and how to find them.. These include compiled service records, pension records, rosters, cemetery records, Internet databases, published books, etc.
- United States Civil War, 1861 to 1865 describes and explains United States and Confederate States records, rather than state records, and how to find them. These include veterans’ censuses, compiled service records, pension records, rosters, cemetery records, Internet databases, published books, etc.
- Mudd, Joseph A. (Joseph Aloysius). With Porter in North Missouri : a chapter in the history of the war between the states. (Bethesda, Maryland : University Publications of America, c1990), FHL fiche 6082549 and With Porter in North Missouri : a chapter in the history of the war between the states. (Iowa City, Iowa : Press of the Camp Pope Bookshop, 1992), FHL book 977.8 M2 digitized
- Ponder, Jerry (Jerry Wayne), 1937-. The 9th Missouri Infantry Regiment C.S.A and the 12th Missouri Infantry Regiment, C.S.A. (Doniphan, Missouri : Ponder Books, c1996), FHL book 977.8 M2po.
- National Park Service, The Civil War Soldiers and Sailors System, (accessed 21 Sept 2011).