In September, 1918, at time of WWI Draft, Leon Leonard Kesner was 39 years old and residing and working in Chicago as a salesman for H&P Sauce Co. Birth was cited as February 2, 1879 in Chicago. He gave next of kin as his mother, Mrs L J Kesner of Chicago.
Cook County, Illinois birth record for Leon Kesner:
1900 US Census; 2 Jun 1900; 3918 Calumet Avenue, Chicago, Cook County, Illinois.
Louis J. Kesner, 59, head, b. Jan 1841 in Holland, married 35 years, mfr. cigars, immigrated 1876
Sarah Kesner, 58, wife, b. Dec 1841 in Holland, married 35 years, mother of 9-7 living, immigrated 1876
Leon Kesner, 21, son, b. Feb 1879 in Illinois, single, city salesman-candy
Francis Kesner, 19, daughter, b. Jan 1881 in Illinois, single
Sol. Kesner, 16, son, b. Apr 1844 in Illinois, at school
Maggie Maloney, 19, servant, b. Jun 1880 in Ireland, single, immigrated 1897 
Lee L Kesner died at the age of 47 on September 17, 1926 at Chicago. Left behind a wife, Stephanie. He was born February 2, 1879 at Chicago to Louis Kesner and Sarah Staal, both of Amsterdam.
Not sure this is the right person:
1910 US Census, 20 Apr 1910; 6242 Washington Avenue, Chicago, Cook County, Illinois.
Leon L Kessner Head M 30 Illinois, married 6 years, real estate manager-for brother, both parents b. in Holland
Ethel L Kessner Wife F 24 Pennsylvania, married 6 years, mother of 1-1 living
Leah H Kessner Daughter F 1 Illinois
Susannah H Newbauer Mother-in-law F 49 Pennsylvania, widowed, mother of 4-4 living, proprietress of delicatessen
John J Newbauer Brother-in-law M 14 Illinois, office boy-awning factory
Henrietta S Newbauer Sister-in-law F 11 Illinois 
↑ United States, Selective Service System. World War I Selective Service System Draft Registration Cards, 1917-1918. Washington, D.C.: National Archives and Records Administration. M1509, 4,582 rolls. Registration State: Illinois; Registration County: Cook; Roll: 1503827; Draft Board: 46. Ancestry.com. U.S., World War I Draft Registration Cards, 1917-1918 [database on-line]. Ancestry Record 6482 #9834504
↑ “Illinois, Cook County Birth Registers, 1871-1915," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:N79R-CFH : 10 March 2018), Leon Kesner, Jan 1879; citing 457, Chicago, Cook, Illinois, Cook County Courthouse, Chicago; FHL microfilm 1,287,723.
↑ "Illinois Deaths and Stillbirths, 1916-1947," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:N3H4-455 : 10 March 2018), Louis Kesner in entry for Lee L. Kesner, 17 Sep 1926; Public Board of Health, Archives, Springfield; FHL microfilm 1,877,895.
↑ "United States Census, 1910," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MKC4-KLG : accessed 22 May 2019), Leon L Kessner, Chicago Ward 7, Cook, Illinois, United States; citing enumeration district (ED) ED 422, sheet 7A, family 185, NARA microfilm publication T624 (Washington D.C.: National Archives and Records Administration, 1982), roll 248; FHL microfilm 1,374,261.