I have no proof that Rollin had an earlier wife, but given his age at his second marriage, he almost certainly had a previous marriage.

1a.  Jordan R. Dodd, ed.  1998.  Marriage Index:  Illinois, 1851-1900.  Liahona Research, Orem, UT (Broderbund CD-250):  no Carroll Co. marriages on CD.

1b.  Illinois Statewide Marriage Index, 1763–1900:  not found.

1c.  Jordan R. Dodd.  Marriage Index:  Michigan and Wisconsin, 1830-1900.  Liahona Research, Orem, UT (Broderbund CD-251):  not found.  CD contains no Rock Co., WI, records.

2.  1880 Census.

3.  Veterans' Schedules:  U.S. Selected States, 1890 (Broderbund CD-131):

1890

Coon, Rolin R.

WI

Rock Co.

Janesville

ED 205

p. 5

deceased

4.  1900 Census.

5a.  Obituary from the Onaga Herald, dated 12 Feb 1920 (courtesy of Merry Pinick):

Fannie E. Myers, daughter of Thomas and Eliza Myers... departed this life on February 6th, 1920... She leaves to mourn her departure, besides the husband, son and grandson, three sisters and three brothers, as follows: Mrs. Ellen Van Alstine, of Chicago, Ill., Mrs. Nellie Grant, of Rockford, Ill., Mrs. Susan Hays of Butte, Mont., Fred Myers, of Wolf Point, Mont., Jacob Coon of Janesville, Wis., and Roy Coon, of Iowa, besides a host of other relatives and friends...

Nellie, Ellen, and Susan are Ralph's half-sisters, children of his mother, Eliza (HOLT) COON, and her first husband, Thomas MYERS.  The question is whether Jacob COON and Roy COON are full-brothers or half-brothers, that is, children of Rollin COON and his first wife or his second wife.

5b.  Obituary from the Janesville Gazette, dated 3 Aug 1920 (courtesy of Brenda Brauner):

R.W. Coon, 44, a resident of this city for nearly forty years passed away...  Besides his wife and children, he leaves to mourn his death one brother, Roy Coon, Cedar Rapids, IA; three sisters, Mrs. Nellie Grant, Rockford; Mrs Ellen Van Alstine, Rockford; Mrs Susan Hayes, Alberton, Mont....

Has Jacob COON died?  Or was the informant simply unaware of him?

6.  WorldConnect (online at RootsWeb.com).

7.  Broderbund.  World Family Trees.  Vol. 55, Pedigree #55; Vol. 62, Pedigree #1935.  Not seen.  Based on the FamilyFinder index (online at Genealogy.com),  both pedigrees contain both names, that is, both Eliza Melvina HOLT and Rollin R. COON.

8.  Janet U. Krompier.  Ancestors of Grace Elisabeth Lane. [link died]   FamilyTreeMaker User Home Page.

Samuel Coon, born August 16, 1833 in Columbia, NY; died November 19, 1916 in Weeping Water, Cass Co., NE; married Sarah Teeple October 09, 1866 in LaSalle County, Illinois. Notes for Samuel Coon: Obituary, Nov 23, 1916; Weeping Water, Cass, NE. The family moved to Scranton, Pennsylvania in 1838, while the family resided near Scranton, his father died, and the mother and children moved to Illinois in 1854, settling near Ottawa [La Salle Co.].  He was married to Miss Sarah Teeple in 1866.  He lived on a farm near Wapello [Louisa Co.], Iowa, and then came to Nebraska in 1874... During the Civil war he enlisted in the 8th Ill Infantry, D Company.  He is survived by his wife, his only son, Omar... his only daughter Cora, his brother William of Lincoln, NE, his brother Silas (Cyrus??) of Rockford [Winnebago Co.], IL and his only grandchild, Rollin Coon.  His age at death 84-2-4.

This Rollin was obviously born far too late to be our subject, but the name is rare, so could there be a connection?  Samuel was the s/o Peter COON/KUHN, s/o Hendrick KUHN.

9.  Emails from Brenda Brauner, Merrie Pinick.