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.~1928), then head of a 7-person household.
Age 12
b. ~1928
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 | 12 |
| Marital Status | Single |
| Birthplace | Illinois |
| 1935 Residence (City) | Chicago City |
| 1935 Residence (County) | Cook |
| Additional Details | |
| Highest Grade | No 6 |
| 1935 Residence | Same Place |
| Birth State | Illinois |
| Birth Country | United States |
| Birthplace (normalized) | illinois |
| Township / Ward | Chicago City |
| Est. Birth Year | ~1928 |
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 |
|---|---|---|---|---|
| William Mcmahon | Son | — | 12 | ~1928 |
| Mary Mcmahon | Daughter | — | 19 | ~1921 |
| Ambrose Mcmahon | Son | — | 25 | ~1915 |
| Theresa Mcmahon | Daughter | — | 7 | ~1933 |
| John Mcmahon | Son | — | 23 | ~1917 |
| Anna Mcmahon | Head | — | 50 | ~1890 |
| Helen Mcmahon | Daughter | — | 16 | ~1924 |
Census Appearances
1930
Cook, Illinois
Son, age 1
Cook, Illinois · implied b. ~1929 — 4 household members
●
Primary link
· ~Confirmed · 2 sources
XGBoost
Household
| Surname | McMahan |
| Given Name | William Jr. |
| Relationship to Head | Son |
| Sex | M |
| Color / Race | White |
| Age | 1 |
| Marital Status | Single |
| Birthplace | Illinois |
| Father's Birthplace | Illinois |
| Mother's Birthplace | Illinois |
| Birth State | Illinois |
| Birth Country | United States |
| Birthplace (normalized) | illinois |
1940
Cook-County, Illinois
Son, age 12
Cook-County, Illinois · implied b. ~1928 — 7 household members
| Surname | McMahon |
| Given Name | William |
| Relationship to Head | Son |
| Sex | M |
| Color / Race | White |
| Age | 12 |
| Marital Status | Single |
| Birthplace | Illinois |
| 1935 Residence (City) | Chicago City |
| 1935 Residence (County) | Cook |
| Highest Grade | No 6 |
| 1935 Residence | Same Place |
| 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 12 · b. ~1928 · Illinois
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Sibling
Theresa Mcmahon
Sibling · 1940 · age 7
Source co-child of head (derived)
● Co-child · derived · ~0.88
Sibling
Helen Mcmahon
Sibling · 1940 · age 16
Source co-child of head (derived)
● Co-child · derived · ~0.88
Sibling
John Mcmahon
Sibling · 1940 · age 23
Source co-child of head (derived)
● Co-child · derived · ~0.88
Sibling
Mary Mcmahon
Sibling · 1940 · age 19
Source co-child of head (derived)
● Co-child · derived · ~0.88
Sibling
Ambrose Mcmahon
Sibling · 1940 · age 25
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-t0627-00956-00340)
| Line | Name | Age | Relation | Occupation | Birthplace |
|---|---|---|---|---|---|
| 1 | William Mccormick | 34 | Head | Sergeant | Ireland |
| 2 | Barbara Mccormick | 34 | Wife | Machine Oper | Indiana |
| 3 | Michael Jasurth | Jaswith | 38 | Head | Drug Clerk | Ireland |
| 4 | Christine Jasurth | Jaswith | 31 | Wife | — | New York |
| 5 | Michael Jr Jasurth | Jaswith | 0 | Son | — | Chicago |
| 6 | Clarence Anderson | 46 | Head | Motorman | Illinois |
| 7 | Lillian Anderson | 47 | Wife | — | Illinois |
| 8 | Franklin Sendran | Sendrau | 49 | Head | Carrier | Illinois |
| 9 | Ruby Sendran | Sendrau | 44 | Wife | — | Illinois |
| 10 | Lois Vrooman | 46 | Head | Barber | Iowa |
| 11 | Irene Vrooman | 38 | Wife | — | Illinois |
| 12 | Leo J Vrooman | 9 | Son | — | Illinois |
| 13 | Arlene Vrooman | 4 | Daughter | — | Illinois |
| 14 | John Miller | 46 | Head | Chef'S Helper | Illinois |
| 15 | Louis Miller | 42 | Brother | — | Illinois |
| 16 | Frank Marjanovich | 48 | Head | Settling Welder | Yugoslavia |
| 17 | Angeline Marjanovich | 40 | Wife | Instructor | Poland |
| 18 | Lillian Marjanovich | 18 | Daughter | Beauty Oper | Chicago |
| 19 | Robert Batchaw | 30 | Head | Parker | Canada |
| 20 | Anne Batchaw | 30 | Wife | Cashier | Illinois |
| 21 | Diane Batchaw | 3 | Daughter | — | Illinois |
| 22 | Richard Wharton | 47 | Roomer | Plumber | Kentucky |
| 23 | Rose Butterfield | 64 | Head | — | Illinois |
| 24 | James Sr Byrne | 59 | Head | Cement Laborer | England |
| 25 | Rachel Byrne | 58 | Wife | — | England |
| 26 | James Jr Byrne | 35 | Son | Sta Fireman | England |
| 27 | Armando Lorenzi | 58 | Head | Proprietor | Italy |
| 28 | Fanny Lorenzi | 51 | Wife | Dressmaker | Italy |
| 29 | Edna Lorenzi | 27 | Daughter | Entertainer | Illinois |
| 30 | Anna Mcmahon | 50 | Head | — | Illinois |
| 31 | Ambrose Mcmahon | 25 | Son | Yard Clerk | Illinois |
| 32 | John Mcmahon | 23 | Son | Loader Baggage | Illinois |
| 33 | Mary Mcmahon | 19 | Daughter | New Worker | Illinois |
| 34 | Helen Mcmahon | 16 | Daughter | — | Illinois |
| 35 | William Mcmahon THIS PERSON | 12 | Son | — | Illinois |
| 36 | Theresa Mcmahon | 7 | Daughter | — | Illinois |
| 37 | Sarah Howard | 56 | Head | Dressmaker | Kentucky |
| 38 | Norma Hardy | 35 | Roomer | Cashier | Alabama |
| 39 | Carl Schott | 54 | Head | Laborer | Germany |
| 40 | Elizabeth Schott | 53 | Wife | — | Germany |
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)