John was born on 23 September 1839 to John Blagdon and Elizabeth Thomas (Hall) Blagdon in Plymouth, Devon, England,  and was baptised 11 October of the same year in Plymouth Charles.  On the 1841 census, his parents were living in Bath Place, and his father was listed as a brickmaker. (The family was misspelled as Blagden.) 
He was still in Bath Place with his parents, aged 11.  By the 1861 census, however, aged 21 and a brickmaker himself, he was living with his parents at 22 Jubilee Street, Plymouth Charles. 
John is listed as a farm labourer in the 1871 census,  but he has changed occupation again by the 1881 census, age 41, and is working as a labourer in HM Dockyard for the next thirty years.  John and Mary Ann (plus children) lived in West Street, Maker for many years during his work, and after Mary Ann died in 1892 he can be found on the 1901 census living with daughter Margaret (Blagdon) Lewis at 17 Duke Street, Devonport.  On the 1911 census he is living alone in one room at 39 George Street, Stonehouse, and describes himself as 'sometimes engaged in basket making'.
↑ UK Birth registration: Plymouth Vol 9 Page 376, December quarter 1839, mother's maiden name HALL
↑ Devon Baptisms [database], Parish baptism register (Plymouth Charles), transcription by Devon Family History Society via findmypast
↑ "England and Wales Census, 1841," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MQTP-81Z : 13 December 2017), John Blagden in household of Jno Blagden, St Andrew, Devon, England; from "1841 England, Scotland and Wales census," database and images, findmypast (http://www.findmypast.com : n.d.); citing PRO HO 107, The National Archives, Kew, Surrey.
↑ "England and Wales Census, 1851," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:SGJQ-26W : 10 November 2017), John Blagdon in household of John Blagdon, St Andrew, Devon, England; citing St Andrew, Devon, England, p. 24, from "1851 England, Scotland and Wales census," database and images, findmypast (http://www.findmypast.com : n.d.); citing PRO HO 107, The National Archives of the UK, Kew, Surrey.
It may be possible to confirm family relationships with John by comparing test results with other carriers of his Y-chromosome or his mother's mitochondrial DNA.
However, there are no known yDNA or mtDNA test-takers in his direct paternal or maternal line.
It is likely that these autosomal DNA test-takers will share DNA with John:
So happy to find this information on my Great Grandad John, my Dad ( son of Alice ) was10 at the time of his Grandfather's death, he never told me whether he met his Grandparents. Dad had the dark hair which I always think is a part of being Devonshire and Cornish heritage. I do wish that I had met some of my Dad's younger Aunts and Uncle. I did meet his Cousin Winifred, Daughter of William Blagdon. My Dad was Frederick John Knight, son of Alice Blagdon. I have always felt " at home " when I have visited the West Country. If anyone reading this is an offspring of my Grand mother Alice's Brothers or Sisters please contact me before it is too late!! I am 87 so time is shortening.