The Illinois State Archives show BLOOMER ARNOLD in the Civil War Records for the 52nd IL. US Infantry. He was 19, lived in Sandwich, DeKalb Co., IL., farmer, born NY, Joined 28 Sept. 1861 Geneva, IL.,for 3 years, and mustered in 19 Nov. 1861 Geneva, IL. Does not show where or when mustered out.
The Archives also show a BLOOMER ARNOLD married ELLEN L. FISH 29 Oct. 1863, DeKalb Co., IL.
There was an Ellen Fish age 13, b. PA. <1847> in Somonauk, DeKalb Co., IL. in 1860 with Horace and Catherine FISH, pg. 31, image 19, while Bloomer ARNOLD age 17 was in Somonauk, DeKalb Co. on pg. 218, image 6.
I was unable to find Ellen(FISH)ARNOLD in 1870 with Bloomer.
She may have died and Bloomer remarried to Adeline NICHOLS.
Possibly "Bloomer" may have been a nickname, although I don't know why he would use it on official records.
Gilbert L. Arnold in 1870 and 1880 DeKalb Co. is a very close fit as far as age to have been the son of Garret and Mary Arnold of LaSalle Co., IL. in 1850.
Arthur T. ARNOLD, s/o Gilbert and Adeline Arnold ends up in Columbus, Franklin Co., Ohio in 1920. He had a son Gilbert b. 1 Sept. 1902 as per the SSDI and died in Columbus July 1980.