Although his gravestone lists his birth year as 1859, It appears from the censuses that he was born in 1860.

Extract from the 1860 Census:
Name: Robert Pinkerton
Age in 1860: 1/12
Estimated birth year: 1859
Birthplace: New York
Race: white
Sex: male
Relation to head-of-house: son
Home in 1860: Hebron, Washington, New York
Post office: West Hebron
Occupation: not listed
Siblings living at home: none
Census place: Hebron, Washington, New York; Roll M653_874; Page: 202; Image: 432; Family History Library Film: 803874
Date: 20 Jun 1860

Extract from the 1870 Census:
Name: Robert Pinkerton
Age in 1870: 10
Estimated birth year: 1860
Birthplace: New York
Race: white
Sex: male
Relation to head-of-house: son
Home in 1870: Dayton, Waupaca, Wisconsin
Post office: Rural
Occupation: attending school
Siblings living at home: Mary A (age 8), Ida (6), Saml J (5), and John (3)
Census place: Dayton, Waupaca, Wisconsin; Roll: M593_1744; Page: 23; Image: 47
Date: 6 Jun 1870

Extract from the 1880 Census:
Name: Robert Pinkerton
Age: 20
Estimated birth year: 1860
Birthplace: New York
Race: white
Sex: male
Relationship to head-of-household: son
Home in 1880: Dayton, Waupaca, Wisconsin
Marital status: single
Father's birthplace: Ireland
Mother's birthplace: Ireland
Occupation: farm laborer
Siblings living at home: Mary Ann (age 18), Ida (16), Samuel (15), and John (13)
Census place: Dayton, Waupaca, Wisconsin; Roll: T9_1451; Family History Film: 1255451; Page: 31.2000; Enumeration District: 163
Date: 22 Jun 1880

Extract from the 1900 Census:
Name: Robert Pinkerton
Age at last birthday: 40
Date of birth: May 1860
Birthplace: Wisconsin [sic]
Race: white
Sex: male
Relationship to head-of-house: head
Home in 1900: Dayton, Waupaca, Wisconsin
Marital status: married
Number of years of marriage: 17
Able to read, write and speak English: yes
Father's birthplace: Ireland
Mother's birthplace: Ireland
Home owned or rented: owned
Mortgage: yes
Farm or home: farm
Occupation: farmer
Census place: Dayton, Waupaca, Wisconsin; Roll: T623 1823; Page: 5A; Enumeration District: 123
Date: 11 Jun 1900

Extract from the 1910 Census:
Name: Robert D Pinkerton
Age in 1910: 49
Estimated birth year: 1861
Birthplace: New York
Race: white
Sex: male
Relationship to head of family: head
Home in 1910: Dayton, Waupaca, Wisconsin
Marital status: married
Number of years of present marriage: 26
Able to speak English: yes
Able to read and write: yes
Father's birthplace: Ireland
Mother's birthplace: Ireland
Home owned or rented: owned; has mortgage
Farm or house: farm
Occupation: farmer
Type of industry: farm
Salary or wage worker: working on own account
Census place: Dayton, Waupaca, Wisconsin; Series: T624; Roll: 1743; Page: 54A; Enumeration District: 70; Part: 1; Line: 3
Date: 5 May 1910

Extract from the 1920 Census:
Name: Robert D Pinkerton
Age: 59
Estimated birth year: 1861
Birthplace: New York
Race: white
Sex: male
Relationship to head of house: brother-in-law
Living with: Edwin and Martha (Stratton) Bailey, ages 70 and 69
Home in 1920: Britt, Hancock, Iowa
Address: Second Street
Marital status: married
Able to speak English: yes
Able to read and write: yes
Father's birthplace: Ireland
Mother's birthplace: Ireland
Occupation: none
Census place: Britt, Hancock, Iowa; Roll: T625_492; Page: 13A; Enumeration District: 143; Image: 113
Date: 13 Jan 1920

Extract from the 1930 Census:
Name: Robert Pinkerton
Age: 69
Estimated birth year: 1861
Birthplace: New York
Race: white
Sex: male
Relation to head-of-house: brother-in-law
Living with: Emma Stratton Brigham, age 83
Home in 1930: Waupaca, Waupaca, Wisconsin
Marital status: married
Age at first marriage: 23
Education: able to speak English
Education: able to read and write
Father's birthplace: Northern Ireland
Mother's birthplace: Northern Ireland
Military service: no
Occupation: none
Census place: Waupaca, Waupaca, Wisconsin; Roll: 2617; Page: ; Enumeration District: 40; Image: 1035.0
Date: 8 Apr 1930

Extract from the 1940 Census:
Name: Robert D Pinkerton
Age: 79
Estimated birth year: 1861
Birthplace: New York
Race: white
Sex: male
Relation to head-of-house: head
Home in 1940: Waupaca, Waupaca, Wisconsin
Address: 515 East Fulton Street
Marital status: married
Highest grade of school completed: 8
Living on farm: no
Home owned or rented: owned
Value of home: $1000
City of residence in 1935: Waupaca, Waupaca, Wisconsin
Resident on farm in 1935: no
Occupation: unable to work
Has other income of more than $50: yes
Census place: Waupaca, Waupaca, Wisconsin; Roll: T627_4535; Page: 1B; Enumeration District: 68-41
Date: 8 Apr 1940

Obituary from the "Post-Crescent" of Appleton, Wisconsin dated 29 Jan 1947:
Funeral Services for
Waupaca Man Thursday
Waupaca - Funeral services for Robert Pinkerton, 87, who died Tuesday in the City hospital after a long illness, will be held at 2 o'clock Thursday afternoon at the Holly Funeral home. Burial will be in Lakeside cemetery with the Rev. A. E. Tink of the First Methodist church in charge.
Survivors are the widow and two sons, Gerald and Claire [sic].

He married (1) Alice Adeline Stratton 3 Mar 1883 in Dayton, Waupaca, Wisconsin.
He married (2) Mary Elizabeth Dixon Mar 1936.