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
Company B - principally recruited from Brooklyn, Kings County
Company C - principally recruited from Hudson, Taghkanick, Copake, Stockport, Livingston, Gallatin, Claverack, Stuyvesant and Germantown
Company D - principally recruited from Brooklyn, Hudson, Fishkill and Ghent
Company E - principally recruited from Ghent, Claverack, Hudson, Copake, Livingston, Hillsdale, Fishkill, Greenport, Stuyvesant and Taghkanick
Company F - principally recruited from Brooklyn and Brook-haven
Company G - principally recruited from Hudson, Kinderhook, Claverack, Stockport, Ghent, Chatham, Taghkanick, New Lebanon, Fishkill and Poughkeepsie
Company H - principally recruited from Brooklyn, Kings County
Company I - principally recruited from Hudson, Poughkeepsie, Gallatin, Livingston, Pleasant Valley and Taghkanick; the second Company G at Hudson
Company K - principally recruited from Brooklyn, Kings County
Civil War Soldiers & Sailors System has the information listed above and may have additional historical information. Searches can be made by name of a soldier or sailor. Information about cemeteries battles, prisoners, medals of honor and national parks is also included.
Phisterer, Frederick. New York in the War of the Rebellion, 1861 to 1865. Albany, New York : J.B. Lyon, 1912. Google Books, other libraries with this book, FHL Collection FHL book 974.7 M2p, FHL film 1486494-1486496
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 Collection FHL book 973 M2ua
- Frederick Henry Dyer, A Compendium of the War of the Rebellion, (Des Moines, Iowa: Dyer Publishing Co., 1908), as cited at Civil War Soldiers & 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)