On 10 May 1919, John R. W. Kopp married Katherine B. Holthauser in Baltimore City, Maryland. He was 23, resident of Baltimore, Maryland, white, no occuption listed, previously married, prior marriage dissolved “by death”; she was 19, resident of Baltimore, Maryland, white, no prior marriage. [State of Maryland, Department of Health, Report of Marriage (no index number).]

On 11 May 1919, The Baltimore Sun published Marriage Licenses, including:
KOPP — HOLSHAUSER — John R. W. Kopp, 23, divorced, 2705 Eastern avenue; Katharine B. Holshauser, 19.
[The Baltimore Sun, 11 May 1919, page C1.]

1920 U.S. Census, Baltimore City, Maryland
Enumeration District 108, 8th Ward, page 19A
2503 East Preston Street
Kopp, John R, head, renter, male, white, 22, married, not in school, can read and write, born in Maryland, both parents born in Maryland, speaks English, foreman in ship yard, wage worker
Kopp, Catherine, wife, female, white, 19, married, not in school, can read and write, born in Virginia, father born in North Carolina, mother born in Germany and speaks German, speaks English, no occupation

1930 U.S. Census, Baltimore City, Maryland
26th Ward, Block 237, Enumeration District 4-407, Supervisor’s District 4, Sheet 5A
Enumerated on 3 April 1930
3401-6 Baltimore Street
Dwelling 46, Household 52
Kopp, John R., head, renting for $38, male, white, age 32, married, first married at age 22, not in school, can read and write, born in Maryland, both parents born in Maryland, speaks English, occupation mechanic with electrical equipment, wage worker, at work previous day, not a veteran
Kopp, Katharine, wife, female, white, age 29, married, first married at age 19, not in school, can read and write, born in Virginia, father born in North Carolina, mother born in Germany, speaks English, no occupation
Kopp, James, son, male, white, age 9, single, in school, born in Maryland, father born in Maryland, mother born in Virginia, no occupation
Kopp, Betty, daughter, female, white, age 6, single, in school, born in Maryland, father born in Maryland, mother born in Virginia, no occupation
Kopp, Katherine, daughter, female, white, age 4/12, single, not in school, born in Maryland, father born in Maryland, mother born in Virginia, no occupation

1936 Baltimore City Directory, page 717:
Kopp John R (Kath H) shtmtlwkr h629 s Savage

1937 Baltimore City Directory, page 694:
Kopp John R (Kath H) sheet metal wkr h 629 Savage1920 U.S. Census, Baltimore City, Maryland
Enumeration District 108, 8th Ward, page 19A
2503 East Preston Street
Kopp, John R, head, renter, male, white, 22, married, not in school, can read and write, born in Maryland, both parents born in Maryland, speaks English, foreman in ship yard, wage worker
Kopp, Catherine, wife, female, white, 19, married, not in school, can read and write, born in Virginia, father born in North Carolina, mother born in Germany and speaks German, speaks English, no occupation

1930 U.S. Census, Baltimore City, Maryland
26th Ward, Block 237, Enumeration District 4-407, Supervisor’s District 4, Sheet 5A
Enumerated on 3 April 1930
3401-6 Baltimore Street
Dwelling 46, Household 52
Kopp, John R., head, renting for $38, male, white, age 32, married, first married at age 22, not in school, can read and write, born in Maryland, both parents born in Maryland, speaks English, occupation mechanic with electrical equipment, wage worker, at work previous day, not a veteran
Kopp, Katharine, wife, female, white, age 29, married, first married at age 19, not in school, can read and write, born in Virginia, father born in North Carolina, mother born in Germany, speaks English, no occupation
Kopp, James, son, male, white, age 9, single, in school, born in Maryland, father born in Maryland, mother born in Virginia, no occupation
Kopp, Betty, daughter, female, white, age 6, single, in school, born in Maryland, father born in Maryland, mother born in Virginia, no occupation
Kopp, Katherine, daughter, female, white, age 4/12, single, not in school, born in Maryland, father born in Maryland, mother born in Virginia, no occupation

1936 Baltimore City Directory, page 717:
Kopp John R (Kath H) shtmtlwkr h629 s Savage

1937 Baltimore City Directory, page 694:
Kopp John R (Kath H) sheet metal wkr h 629 Savage

1940 U.S. Census, Parkville, Baltimore County, Maryland
Enumeration District 3-56A, page 12
7444 Park Drive, Household 39, owned, value of home $3,800, not on a farm
Kopp, John R. W., head, male, white, 42, married, not in school, highest level of education 4 years of high school, born in Maryland, resided in Baltimore, Maryland in 1935, did not live on a farm in 1935, employed for pay, worked 40 hours week prior to the census, occupation sheet metal in electrical implements industry, private work, worked 52 weeks in 1939, income $2,450, no other sources of income
Kopp, Katherine, wife, female, white, 39, married, not in school, highest level of education 2 years of high school, born in Virginia, resided in Baltimore, Maryland in 1935, did not live on a farm in 1935, home housework, no other income
Kopp, James F., son, male, white, 19, single, not in school, highest level of education 4 years of high school, born in Maryland, resided in Baltimore, Maryland in 1935, did not live on a farm in 1935, worked 40 hours week prior to the census, occupation aerospace mechanic for plane factory, private work, worked 52 weeks in 1939, income $1,000, no other sources of income
Kopp, Elizabeth K., daughter, female, white, 16, single, in school, highest level of education 1 year of high school, born in Maryland, resided in Baltimore, Maryland in 1935, did not live on a farm in 1935, not employed, no other sources of income
Kopp, Kay D., daughter, female, white, 10, single, in school, highest level of education 4th grade, born in Maryland, resided in Baltimore, Maryland in 1935, did not live on a farm in 1935