66th Regiment, Enrolled Missouri Militia (Union)
The 66th Regiment, Enrolled Missouri Militia enrolled between 22 July 1862 and 26 November 1862. They were ordered into service between 6 August 1862 and 29 November 1862. The regiment was first discharged between 30 April 1862 and 21 February 1863. They were ordered into service again on 30 April 1863. They were then discharged on 31 October 1864. The Colonel in charge was Colonel Oliver T. Phillips. 
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 A - Captain Henry C. Calfee - Many men from Wintersville, Sullivan County
Company B - Captains Warren McCullough and Peter Setters - Many men from Sullivan County
Company C - Captain Dennis Adams - Many men from Sullivan County
Company D - Captain Victor Doze - Many men from Greencastle, Sullivan County
Company E - Captains William H. Dearing and E. L. Webb - Many men from Milan, Sullivan County
Company F - Captain James K. Martin - Many men from Kiddesville, Sullivan County
Company G - Captain Johnson W. Jewett - Many men from Milan, Sullivan County
Company H - Captain Daniel LaFever - Many men from Milan, Sullivan County
Company I - Captain John W. Beck - Many men from Sullivan County
Company K - Captain Reuben F. (R. F.) Canterbury - Many men from Milan, Sullivan County
The above information about the companies with partial rosters is found in Kenneth E. Weant's book, Civil War Records: Missouri Enrolled Militia Infantry Regiments, Volume 9 
- 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.
- Kenneth E. Weant, Civil War Records:Missouri Enrolled Militia Infantry Regiments, Volume 9 (Arlington, Texas : K.E. Weant, c2010), pages 18-30. FHL book 977.8 M2wka v. 9