| | Her married name was Zimmerman.2 |
| | Mary O'Brien was also known as Margaret.3 |
Birth* | circa 1873 | She was born circa 1873 at St. Louis, Missouri.1 |
| 2 June 1880 | She appeared on the census of 2 June 1880 in the household of Margaret Purtell at 1416 Cass Avenue (rear), St. Louis, Missouri, age 7, b. MO.4 |
| 1 June 1900 | She appeared on the census of 1 June 1900 in the household of Edward O'Brien at 4357 North Market Street, St. Louis, Missouri, sister, age 25, b. MO Feb 1875, single.5 |
Marriage* | circa 1922 | She married Albert Zimmerman circa 1922.2 |
| 8 April 1930 | She and Albert Zimmerman appeared on the census of 8 April 1930 at 2226 Mullanphy Street, St. Louis, Missouri.2 |
| 16 April 1940 | She appeared on the census of 16 April 1940 in the household of Frank O'Brien at 2226 Mullanphy Street, St. Louis, Missouri, as Margaret Zimmerman, age 64, b. MO, same res. in 1935.6 |