WM
William Mcmahon — 1940 US Census Record
Linked across censuses1940 United States Federal Census · Cook-County, Illinois
Our Model Tree links this William Mcmahon across the 1930 and 1940 US Censuses in Cook-County, Illinois (XGBoost, ~Confirmed) — first a son (b.~1923), then head of a 7-person household.
Age 17
b. ~1923
Male
Son
Born: Illinois
Single
1940 Census Record Details
| Census Year | 1940 |
| Location | Cook-County, Illinois |
| Surname | McMahon |
| Given Name | William |
| Relationship to Head | Son |
| Sex | M |
| Color / Race | White |
| Age | 17 |
| Marital Status | Single |
| Birthplace | Illinois |
| 1935 Residence (City) | Chicago City |
| 1935 Residence (County) | Cook |
| Additional Details | |
| Income (1939) | 0 |
| Highest Grade | H-1 |
| 1935 Residence | Same house |
| Birth State | Illinois |
| Birth Country | United States |
| Birthplace (normalized) | illinois |
| Township / Ward | Chicago City |
| Est. Birth Year | ~1923 |
Household Members
Census records only state relationship to the household head.
Pairwise kinship is derived (~90–95% accurate), not recorded.
Step/blended families and boarders can break it.
7 people recorded at the same address in the 1940 census.
| Name | Relation to head | Relative to William | Age | Birth yr |
|---|---|---|---|---|
| Mary Mcmahon | Spouse | — | 46 | ~1894 |
| William Mcmahon | Son | — | 17 | ~1923 |
| James Mcmahon | Head | — | 45 | ~1895 |
| Marion Mcmahon | Daughter | — | 21 | ~1919 |
| Joan Mcmahon | Daughter | — | 23 | ~1917 |
| Morris Mcmahon | Son | — | 26 | ~1914 |
| James Mcmahon | Son | — | 20 | ~1920 |
Census Appearances
1930
Cook, Illinois
Son, age 6
Cook, Illinois · implied b. ~1924 — 5 household members
●
Primary link
· ~Confirmed · 2 sources
XGBoost
Household
| Surname | McMahon |
| Given Name | William Jr. |
| Relationship to Head | Son |
| Sex | M |
| Color / Race | White |
| Age | 6 |
| Marital Status | Single |
| Birthplace | Illinois |
| Father's Birthplace | Scotland |
| Mother's Birthplace | Scotland |
| Occupation | none |
| Birth State | Illinois |
| Birth Country | United States |
| Birthplace (normalized) | illinois |
1940
Cook-County, Illinois
Son, age 17
Cook-County, Illinois · implied b. ~1923 — 7 household members
| Surname | McMahon |
| Given Name | William |
| Relationship to Head | Son |
| Sex | M |
| Color / Race | White |
| Age | 17 |
| Marital Status | Single |
| Birthplace | Illinois |
| 1935 Residence (City) | Chicago City |
| 1935 Residence (County) | Cook |
| Income (1939) | 0 |
| Highest Grade | H-1 |
| 1935 Residence | Same house |
| Birth State | Illinois |
| Birth Country | United States |
| Birthplace (normalized) | illinois |
Model Tree
An inferred pedigree reconstructed from census links — up to 4 generations within the 1900–1950 window. Closer generations are built from household co-residence; deeper ones are bridged by following a relative to their own childhood census. Confidence compounds and weakens with each generation.
Our Model Tree links William Mcmahon across 2 US Census years (1930 and 1940) in 2 locations, using XGBoost record linkage.
Show:
This person
Anchor record
William Mcmahon
Son · 1940 · age 17 · b. ~1923 · Illinois
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Sibling
Morris Mcmahon
Sibling · 1940 · age 26
Source co-child of head (derived)
● Co-child · derived · ~0.88
Sibling
James Mcmahon
Sibling · 1940 · age 20
Source co-child of head (derived)
● Co-child · derived · ~0.88
Sibling
Marion Mcmahon
Sibling · 1940 · age 21
Source co-child of head (derived)
● Co-child · derived · ~0.88
Sibling
Joan Mcmahon
Sibling · 1940 · age 23
Source co-child of head (derived)
● Co-child · derived · ~0.88
Confirmed / household (~0.90+)
Probable / derived (~0.65–0.89)
Candidate (<0.65, unverified)
Original Census Page
1940 US Federal Census — Cook-County, Illinois
Open full size
1940 US Federal Census — Cook-County, Illinois
Page Contents
40 people indexed on this census page (nara:1940:m-t0627-00947-00537)
| Line | Name | Age | Relation | Occupation | Birthplace |
|---|---|---|---|---|---|
| 1 | James Mcmahon | 45 | Head | Motorman | Irish Free State |
| 2 | Mary Mcmahon | 46 | Wife | — | Illinois |
| 3 | Morris Mcmahon | 26 | Son | Telephone Clerk | Illinois |
| 4 | Joan Mcmahon | 23 | Daughter | Telephone Operator | Illinois |
| 5 | Marion Mcmahon | 21 | Daughter | Telephone Operator | Illinois |
| 6 | James Mcmahon | 20 | Son | Printers Helper | Illinois |
| 7 | William Mcmahon THIS PERSON | 17 | Son | — | Illinois |
| 8 | Richard Sparr | 48 | Head | Machinist | Illinois |
| 9 | Loretta Sparr | 47 | Wife | — | Illinois |
| 10 | Dorothy Sparr | 25 | Daughter | Weaver | Illinois |
| 11 | Lillian Sparr | 20 | Daughter | Factory Hand | Illinois |
| 12 | Richard Sparr | 16 | Son | — | Illinois |
| 13 | Loretta Sparr | 12 | Daughter | — | Illinois |
| 14 | Anton Garklaski | 72 | Head | — | Lithuania |
| 15 | William Lion | 35 | Head | Motorman | Illinois |
| 16 | Sylvia Lion | 34 | Wife | — | Illinois |
| 17 | Bill Lion | 8 | Son | — | Illinois |
| 18 | Ruth Lion | 5 | Daughter | — | Illinois |
| 19 | Mary Drenanek | 61 | Mother-in-law | — | Illinois |
| 20 | Charles Mcbreathwaite | 60 | Head | — | Michigan |
| 21 | Emilie Mcbreathwaite | 54 | Wife | — | Illinois |
| 22 | Robert Mcbreathwaite | 30 | Son | Foreman | Illinois |
| 23 | Kyle W. Mcbreathwaite | 16 | Son | — | Illinois |
| 24 | Albert Sappenfield | 22 | Son-in-law | Maintenance Mechanic | Illinois |
| 25 | Florence Sappenfield | 22 | Daughter | — | Illinois |
| 26 | Alberta Sappenfield | 1 | Granddaughter | — | Illinois |
| 27 | Julia Tucand | 63 | Lodger | Practical Nurse | Kansas |
| 28 | Robert Zonke | 57 | Head | Optician | Illinois |
| 29 | Augusta Zonke | 55 | Wife | — | Illinois |
| 30 | Dorothy Zonke | 21 | Daughter | Factory Hand | Illinois |
| 31 | Howard Dithuton | 62 | Head | Watchman | Massachusetts |
| 32 | Ida Dithuton | 62 | Wife | — | Illinois |
| 33 | John Keller | 37 | Son-in-law | Salesman | Illinois |
| 34 | Lillian Keller | 35 | Daughter | — | Illinois |
| 35 | Barbara Ann Keller | 5 | Grandchild | — | Illinois |
| 36 | Ruth J. Keller | 0 | Grandchild | — | Illinois |
| 37 | Martha Schreiber | 55 | Head | — | Illinois |
| 38 | Lillie Schreiber | 55 | Wife | — | Illinois |
| 39 | Matthew Jr. Schreiber | 31 | Son | Boiler Cleaner | Illinois |
| 40 | Frank Jerzak | 45 | Head | Office Clerk | Wisconsin |
About This Record & Model Tree
This record was independently indexed by YourRoots from the 1940 United States Federal Census (NARA). Our Model Tree links this person across census decades using XGBoost-based record linkage, with per-link confidence scores. Household corroboration strengthens the signal when co-residents appear on the same census pages in multiple years.
Source: National Archives and Records Administration (NARA)