Warren doesn't seem to be in 1860 Grant Co. There is a census record of a Warren Cushman in 1860 Mifflin, Iowa Co., WI, Pg. 779.
He does appear in 1870 Grant Co.
1870 Census, Fennimore, Grant, WI, Pg. 130, Household 224:
Warren Cushman, 38, Farmer, $1800, $775, PA
Lucinda, 35, Keeps House, PA
Chester, 11, At School, WI
Ella, 9, At School, WI
Myrta, 3/13, WI (born in March 1870)
Hester McClenehan, 55, At Home, PA
William Russell, 22, Laborer, WI
Carrie, 21, Keeps House, WI
Is Hester the mother of Lucinda?
Is your Warren Cushman the son of Barnabas and Polly (Cory) Cushman? There is a lengthy biography of a Harvey Cushman, born in Waterford, Erie, PA on 29 Oct 1839 in the 1901 Commemorative Biographical Record of the Counties of Rock, Green, Grant, Iowa and Lafayette WI. This Harvey had a brother named Warren who was in Kansas in 1901.
If this matches up, let me know and I can sent you a transcript of the bio.
There was a Warren Cushman in 1880 Mifflin, Iowa, WI, but his age and wife doesn't seem to match. Here seems to be yours:
1880 Census, Lincoln, Smith, KS, Pg. 448
Warren Cushman, 49, Farmer, NY, VT, VT
Lucinda, 46, Keeping House, PA, PA, PA
Ella, 17, WI, NY, PA
Murty V., 10, WI, NY, PA
On the same page is:
Chester Cushman, 21, Farmer, WI, NY, PA
Hope this helps.