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William Brennan - line 42
Source - Year: 1900; Census Place: Waterloo, Black Hawk, Iowa; Roll: T623_418; Page: 20A; Enumeration District: 22
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William Brennan - line 20
Source - Year: 1910; Census Place: Waterloo Ward 4, Black Hawk, Iowa; Roll: T624_392; Page: 16A; Enumeration District: 0026; Image: 911; FHL Number: 1374405.
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Source - Year: 1915; Iowa State Census Collection, 1836-1925; Census Place: Waterloo, Black Hawk, Iowa; Roll: IA1915_35; Image: 3400
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Source - World War I Draft Registration Cards, 1917-1918; Registration Location: Waterloo, Black Hawk, Iowa; Roll: 1643355; Draft Board: 0.
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William Brennan - line 24
Source - Year: 1920; Census Place: Waterloo Ward 4, Black Hawk, Iowa; Roll: T625_478; Page: 8A; Enumeration District: 30; Image: 1031.