Here's an awesome link to a project of the State Historical Society... 
Wisconsin Volunteers: War of the Rebellion, 1861-1865

WHERE TO WRITE FOR COPIES OF U.S. MILITARY RECORDS?

American Civil War, 1861–1865
Enumeration of Civil War Veterans, 1885; 1895; 1905
Special 1890 Census for Florence County Veterans
Spanish-American War, 1898
Philippine-American War, 1899–1902
World War I, 1914–1918 (U.S.,1917–1918) 
U.S. Naval Deaths, World War I
World War II, 1939-1945 (U.S.,1941-1945) 
World War II Draft Registration Cards
Pearl Harbor Casualties (U.S.) 
Korean War, 1950–1953
Vietnam War, 1961–1973
Persian Gulf War, 1990–1991
Alphabetical GRAVE REGISTRATION information
Wisconsin Veterans' Home—Waupaca County

The following is a  database at Ancestry.com in the "subscription section".  If you do not have a subscription and would like me to search the site, emial me with the database name and the person's name that you are researching.

Special Schedule 1890 Census
Surviving Soldiers, Sailors, and Marines, and Widows. etc. 
Commonwealth, Florence County, Wisconsin 
Enumerated June 1890 
(NOTE:  This is only a partial listing....more to follow.)

Name:  PARMENTER, Albert M. 
House Number: #1 
Family Number: #1 
Rank: Private 
Company: K 
Name of Regiment or Vessel: 14th New York H.A. 
Date of Enlistment: 7 December 1863 
Date of Discharge: 13 May 1865 
Lenght of Service: 1 year/5 months/6 days 
Post Office Address: Commonwealth, Wisconsin 
Disability Incurred: 
Remarks:
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Name:  MITCHELL, Robert 
House Number: #57 
Family Number: #65 
Rank: Private                                Company: C 
Name of Regiment or Vessel: 17th Illinois Infantry 
Date of Enlistment: 25 May 1861 
TRANSFERRED TO MISSISSIPPI        10 May1863 
Date of Discharge: 13 June 1864 
Lenght of Service: 2 years 7 months 16 days 
Post Office Address: Commonwealth, Wisconsin 
Disability Incurred: 
Remarks:
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Name:  BE_N_SO, John 
House Number: #58 
Family Number: #66 
Rank: Private                                Company: B 
Name of Regiment or Vessel: 44th New York Infantry 
Date of Enlistment: 5 September 1864 
TRANSFERRED TO E 146 NEW YORK INFANTRY 
Date of Discharge: 3 June 1865 
Lenght of Service: 8 months/28 days 
Post Office Address: Commonwealth, Wisconsin 
Disability Incurred: 
Remarks:
-------------------------------------------------------------------------------
Name:  PARMENTER, Albert M. 
House Number: #1 
Family Number: #1 
Rank: Private                                Company: K 
Name of Regiment or Vessel: 14th New York H.A. 
Date of Enlistment: 7 December 1863 
Date of Discharge: 13 May 1865 
Lenght of Service: 1 year/5 months/6 days 
Post Office Address: Commonwealth, Wisconsin 
Disability Incurred: 
Remarks:

Wisconsin Veterans' Home—Waupaca County
The National Archives has a separate list of Union soldiers who were buried at the United States Soldiers' Home in the period 1861 through 1918. Other separate lists name Union soldiers buried in national cemeteries, 1861 to 1865, with a few as late as 1886. These are arranged by name of cemetery, by military organization, and, for certain states, by name of the soldier. The name indexes are available for Connecticut, Delaware, District of Columbia, Iowa, Maine, Maryland, Massachusetts, Michigan, New Hampshire, New Jersey, Pennsylvania, Rhode Island, Vermont, and Wisconsin.

World War II Draft Registration Cards
A draft administered by the Selective Service System was re-inaugurated during World War II. Until recently, the registration cards for this war were stored in federal records centers and were not generally accessible, but some National Archives regional archives are now processing them  and making them ready for examination. For example, the National Archives regional archives (Great Lakes region) at Chicago already has processed and made available the cards for Illinois, Indiana, Michigan, Ohio, and Wisconsin. Inquiries should be made at the regional archives nearest the place where registration occurred  Other Selective Service System documents of a local or regional nature, dating from 1940, may be found in some National Archives regional archives  and sometimes fragments can be found among the holdings of state archives. Included in some of these holdings are lists of names of individuals who were sent to conscientious objectors' work camps in lieu of military service .   Wisconsin   M559

Alphabetical Grave Registration
An alphabetical graves registration of deceased veterans from the nineteenth century through December 1969 is available at the Department of Veterans Affairs, 77 North Dickinson Street, Madison, Wisconsin 53705. This department also has service records of soldiers of the Spanish-American War, World War I, and World War II.

Enumeration of Civil War Veterans, 1885; 1895; 1905. Special state censuses were taken using returns from county clerks listing veterans residing in Wisconsin during each of the three years shown above. Included are name, rank, and post office. Also included is name of unit or vessel; arranged alphabetically by county and thereunder by local military unit. The 1905 enumeration arranged the names alphabetically by Wisconsin military unit; organizations of other states; United States regular army; "colored" organizations; sailors; marines. These censuses are available in published volumes.