There is a lot of uncertainty about the birth year of Mary and
her twin sister Teresa. In the 1880 census, they are 20 years old,
and listed before their sister Agnes, who is age 12. But from
there on, their ages in censuses aren't consistent.
They're age 30, born June 1869 in the 1900 census (taken June 2, 1900),
age 36 in the 1910 census (taken April 30), 45 in 1920 (taken Jan. 3),
and age 49 in 1930 (taken April 2). I'm using June from the 1900
census, but the year of 1860 from the 1880 census since that is
the census closest to their birth year, and they were listed as
being older than Agnes.
Census: 1920, Rock Island,Illinois