The 1880 census I found shows this: White Oak Township, Gallatin Co, IL, p.475B William Matherly age 37, born TN, parents born TN occupation: Keeps Dry Goods Store Nancey-wife, age 29 born TN, parents born TN William-son, age 12, born IL, occupation: farm laborer Fannie-dau., age 8, born IL James-son, age 6, born IL Lillia-dau., age 2, born IL Floi-dau., age 6 mos., born IL
In 1900, William Matherly was still living in Gallatin Co, IL: William Matherly-55, (born Dec 1844 TN) Lillian M.-22, dau. (b.Apr 1878 IL) Annie-17, dau. (b.Oct 1882 IL) Georgia E.-15, dau. (b.Apr 1885 IL)
Living close by was: James M. Matherly-28 (b.Apr 1871 IL) Mary-30 (b.IL) Harry-8 (b.IL) Addie-6 (b.IL) Mattie-4 (b.IL)
In 1920, Wm. Matherly was living with daughter and son in law: Joseph Fox and wife Fannie (Matherly) Fox in Gallatin Co, IL.
Haven't been able to find him in 1850, 1860 or 1870, but then I don't have good census indexes available for those years.