Notes:

1900 US Federal Census;
This census really had their names misspelled, but all of the data is consistent:

Source Citation: Year: 1900; Census Place: Chicago Ward 9, Cook, Illinois; Roll: T623 254; Page: 2A; Enumeration District: 237.

Name: Otto Saccek
Home in 1900: Chicago Ward 9, Cook, Illinois
Age: 4
Estimated Birth Year: abt 1896
Birthplace: Illinois
Relationship to head-of-house: Son
Father's Name: Vaclav
Mother's Name: Barta
Race: White
Occupation: View Image
Neighbors: View others on page
Household Members: Name Age
Vaclav Saccek 42
Barta Saccek 33
Lillie Saccek 12
Adela Saccek 12
Kamila Saccek 6
Otto Saccek 4
Logla Saccek 2

1910 US Federal Census for Chicago City, Cook, IL He is 13.
1910 Census:

Source Citation: Year: 1910; Census Place: Chicago Ward 10, Cook, Illinois; Roll: T624_251; Page: 33A; Enumeration District: 538; Image: 798.

Name: Otto Zajicek
Age in 1910: 13
Estimated Birth Year: abt 1897
Birthplace: Illinois
Relation to Head of House: Son
Father's Name: Vaclav
Father's Birth Place: Austria
Mother's Name: Barbora
Mother's Birth Place: Austria
Home in 1910: Chicago Ward 10, Cook, Illinois
Race: White
Gender: Male
Neighbors: View others on page
Household Members: Name Age
Vaclav Zajicek 54
Barbora Zajicek 44
Lillie Zajicek 21
Adela Zajicek 21
Kamila Zajicek 16
Otto Zajicek 13
Olga Zajicek 11
William Zajicek 9
Blanche Zajicek 6

Military Registration gives DOB He was single when he registered.

World War I Draft Registration Cards, 1917-1918 World War I Draft Registration Cards, 1917-1918
Name: Otto Zajicek
City: Chicago
County: Cook
State: Illinois
Birthplace: Illinois;United States of America
Birth Date: 1 Jun 1896
Race: White
Roll: 1493574
DraftBoard: 24

Source Citation: Registration Location: Cook County, Illinois; Roll: 1493574; Draft Board: 24.

1920 Federal Census for Ward 10 Chicago City, Cook County, IL. He is 23 & single living with his parents & siblings. This was taken on 2nd day of January 1920. Then on the 10th & 12th days of January, 1920, he is listed with Anna, also 23, his wife. So he must have married between the 2nd & 12th of January, 1920.

1920 United States Federal Census 1920 United States Federal Census
Name: Otto Jakreck
[Otto Zajicek]
Home in 1920: Chicago Ward 10, Cook (Chicago), Illinois
Age: 23 years
Estimated birth year: abt 1897
Birthplace: Illinois
Relation to Head of House: Son
Father's Name: James
Father's Birth Place: Bohemia
Mother's Name: Barbara
Mother's Birth Place: Bohemia
Marital Status: Single
Race: White
Sex: Male
Able to read: Yes
Able to Write: Yes
Image: 1000
Neighbors: View others on page
Household Members: Name Age
James Jakreck 63
Barbara Jakreck 53
Camile Jakreck 26
Otto Jakreck 23
Olga Jakreck 21
Blanche Jakreck 16

Source Citation: Year: 1920;Census Place: Chicago Ward 10, Cook (Chicago), Illinois; Roll T625_318; Page: 2A; Enumeration District: 622; Image: 1000.

1930 United States Federal Census 1930 United States Federal Census
Name: Otto Zajicek
Home in 1930: Chicago, Cook, Illinois
View Map
Age: 34
Estimated birth year: abt 1896
Birthplace: Illinois
Relation to Head of House: Head
Spouse's name: Theresa
Race: White
Household Members: Name Age
Otto Zajicek 34
Theresa Zajicek 34
Clarence Zajicek 12
Eleanor Zajicek 7

Source Citation: Year: 1930; Census Place: Chicago, Cook, Illinois; Roll 450; Page: 8A; Enumeration District: 779; Image: 367.0.

U.S. World War II Draft Registration Cards, 1942 U.S. World War II Draft Registration Cards, 1942
Name: Otto Tony Zajicek
Birth Date: 1 Jun 1896
Birth Place: Chicago
Residence: Chicago, Illinois
Race: White
Roll: 30955_166017

Source Citation: Roll 30955_166017; Local board: Chicago , Illinois.

Social Security Death Index Social Security Death Index
Name: Otto Zajicek
SSN: 312-05-7820
Last Residence: 60068 Park Ridge, Cook, Illinois, United States of America
Born: 1 Jun 1896
Died: Oct 1972
State (Year) SSN issued: Indiana (Before 1951 )

Source Citation: Number: 312-05-7820;Issue State: Indiana;Issue Date: Before 1951.

Source Information:

Ancestry.com. Social Security Death Index [database on-line]. Provo, UT, USA: The Generations Network, Inc., 2007. Original data: Social Security Administration. Social Security Death Index, Master File. Social Security Administration.

NOT OURS:

1930 Federal Census for Berwin City, Cook COunty, IL. He is 33 & married with a daughter.

Name: Otto Zajicek
Home in 1930: Berwyn, Cook, Illinois
Age: 33
Estimated Birth Year: abt 1897
Birthplace: Illinois
Relation to Head of House: Head
Spouse's Name: Anna
Race: White

Household Members: Name Age
Otto Zajicek 33
Anna Zajicek 33
Jane V Zajicek 8

Source Citation: Year: 1930; Census Place: Berwyn, Cook, Illinois; Roll: 414; Page: 15A; Enumeration District: 2005; Image: 417.0.

Family/Spouse: Terezie "Theresa" KOSIK. Terezie was born about 1896 in IL. [Group Sheet] [Family Chart]