There were two photographers in the cabinet card era with the name George Killion. One had a studio in East Saint Louis, IL. The other was George Killion who worked in New York and was apparently never in East Saint Louis.
The George Killion from East Saint Louis, IL, worked as photographer from about 1905 to 1920 apparently always at 343 Collinsville.
George W Killion
(1848 - 1923)
Washington IN, US census, George W Killion is born to Silas D Killion and Catherine Overshiner
1870 Apr 02
Jackson, IL, US census, Killion as farmer living with parents
1880 Jun 11
Ava, Jackson, IL, US census Killion as a barber
Saint Louis, MO, city directory Killion NOT listed
Washington, IN, state records, US census, George W Killion is born to Silas Killion and Catherine Overshiner
US census, G W Killion marriage to Caroline B Kirkpatrick
East Saint Louis, MO, US census G W Killion as barber; res 343 Collinsville av
1905, 1906, 1907
East Saint Louis, IL, city directory, as photographer at 343 Collinsville av
1910 19 Apr
East Saint Louis, IL, US census as photographer at 343 Collinsville av
1920 Jan 05
East Saint Louis, IL, US census, as photographer at 343 Collinsville
1923 Jul 22
East Saint Louis, IL, state records, G W Killion dies at age 75
The records are very thin but based on the few documents found, George Killion was a barber from 1880 to 1900. Sometime between 1900 and 1906 he opened a photograph studio in his home at 343 Collinsville, IL.
All later records find him at the same address as a photographer until his death in 1923.
It is quite possible that he worked for other photographer studios before 1906, learning the trade, and even while he worked at this own studio in later years, but there are no records so far that substantiate this.