I couldn't find much.
1900 MT Custer Co Miles City
Casey- Wm John born July 1854, age 45, married 15yrs, born England, father born England, mother born Canada(English), Naturalized citizen, Engineer
Casey-Bertha E born Sept 1860, age 39, mar15yrs, born Germany, both parents born Germany, mother of 7 children all 7 alive today.
Charles E 1883 born Montana, father born England, mother born Germany
Helen 1884 all children same- born MT, father born Eng, mother Germ
**Note that Charles & Helen were born before marriage. Perhaps they are from a former marriage of Bertha's. They list father's birthplace as England.
Of interest is next door neighbor also named Casey. I can not see an immediate relationship.
Casey, Frank born Mar 1859 Mass, parents born Ireland butcher
Jennis born 1868 NY, parents born Ireland
Frank age 11 all born Montana
John age 10
Belle age 2
Curley, Wm brother born 1880 MT, parents Ireland
1910 MT Custer Co Miles Ward (this census is very hard to read)
Casey, W J age55 mar25 born Eng, father born Eng, mother born Canada, occupation Engineer Stationary
indexed as Mytt J but you can tell it's Bertha
age48 mar25 mother of 7, 6 alive today, born Germany, parents Germany
Charles Edward son 27 MT Eng Germany, Engineer Stationary
..Helton sp?, Caroline daug 26
WJ Jr. son 17
Bertha daug 14
Albert son 10
Prince, John lodger 20 single born Florida laborer
Harrison, Amelia sp? granddaughter age 2
1920 MT Custer Miles Ward
William J Casey 63 widowed rents immigration in 1881, naturalized in 1884, born England, father born Eng, mother born Eng occupation janitor at State Bank.
Charles E & wife Mary C are living at Fort Keough
1930 MT Custer Ft Keough Experiment Station
Casey, Charles E age 47 born abt 1883 MT, England, Germany laborer at Experiment Station
Mary C age 45
Curtis W 19
Estella M 17
Floyd C 15
Montana death index
Charles E Casey died 1956