159th Regiment, New York Infantry
The 159th regiment, also known as the 2nd Dutchess and Columbia Regiment", was Organized at New York City and mustered in November 1, 1862 under Colonel Homer A. Nelson, Lieutenant-Colonel Edward L. Molineux and Major Gilbert A. Draper. The regiment were mustered out at Augusta, Georgia, October 23, 1865. 
The New York State Military Museum website has a unit history project page for the 159th Infantry Regiment.
The Civil War in the East website gives a timeline for the involvement of 159th New York Infantry Regiment in the war.
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.
See the Regiment Roster, for listing of individuals, their company and their involvement.
Company A - principally recruited from Hudson, Greenport, New Lebanon, Livingston, Claverack and Ghent, all in Columbia County
Company B - principally recruited from Brooklyn, Kings County
Company C - principally recruited from Hudson, Taghkanick, Copake, Stockport, Livingston, Gallatin, Claverack, Stuyvesant and Germantown, all in Columbia County
Company H - principally recruited from Brooklyn, Kings County
Company I - principally recruited from Hudson, Gallatin, Livingston, and Taghkanick, all in Columbia County; Poughkeepsie and Pleasant Valley of Dutchess County ; the second Company G at Hudson, Columbia County
Company K - principally recruited from Brooklyn, Kings County
Beginning United States Civil War Research gives steps for finding information about a Civil War soldier. It covers the major records that should be used. Additional records are described in ‘New York 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.
New York in the Civil War describes many Confederate and Union sources, specifically for New York, 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.
The Union Army : a History of Military Affairs in the Loyal States, 1861-65, Records of the Regiments in the Union Army, Cyclopedia of Battles, Memoirs of Commanders and Soldiers, Reprint of original published: Madison, WI.: Federal Pub. Co., 1908. Other libraries with this book,FHL Books 973 M2ua, vols. 1-9
Tiemann, William Francis. The 159th Regiment Infantry New York State Volunteers, in the war of the rebellion, 1862-1865. Bethesda, Md.: University Publications of America,1992 (originally published: Brooklyn, N. Y.: W. F. Tiemann,1891). Google Books, FHL Film 1549968 FHL Fiche 6083854 (3 fiche)
Duffy, Edward. History of the 159th Regiment, N. Y. S. V. .Bethesda, Md.: University Publications of America,1992 (originally reprinted from the Hudson Gazette, 1865. New York: [s.n.], 1890). Online version, FHL Film 2055173 Item 7FHL Fiche 6083853
- Frederick Henry Dyer, A Compendium of the War of the Rebellion, (Des Moines, Iowa: Dyer Publishing Co., 1908), as cited at Civil War Soldiers &amp;amp;amp;amp;amp;amp; Sailors System (database on-line) at http://www.itd.nps.gov/cwss/ (accessed 2010).
- New York State Division of Military and Naval Affairs. "Unit History Project : 159th Infantry Regiment” in New York State Military Museum and Veterans Research Center at http://dmna.state.ny.us/historic/reghist/civil/infantry/159thInf/159thInfMain.htm (accessed 22 December 2010) citing Frederick Phisterer, New York in the War of the Rebellion, 3rd ed. (Albany, N.Y.: J. B. Lyon Company, 1912).
- Hawks, Steve.The Civil War in the East. Database. http://www.civilwarintheeast.com/USA/NY/NY159.php (accessed 22 December 2010)