William Johnston & Jane Dobson - When did they emigrate?
Research note by Wesley Johnston, begun 2 Oct 2018, last updated 4 Oct 2018
www.ancestry.com/mediaui-viewer/collection/1030/tree/34820597/person/172031640702/media/4695a310-48e7-40a8-bae4-683ae01391af
 
Context
First, while I may be a DNA relative (not yet known) of William Johnston, we have no documented relationship. This family's history falls within the scope of my Pre-Confederation Canada Johnstons project.
The 1851 Canada census (actually done in 1852) of Brant Township in Bruce County, Canada West (now Ontario) shows William and Jane and all of their children except 3-year-old Samuel born in Ireland. However later records show most of the children born in Canada. Thus this research note brings together the different records, in order to make evidence-based conclusions from the conflicting evidence.
In general, records closer in time to the event (in this case, the births of the children), tend to be more accurate. However, if the earliest record disagrees with all other records and the earliest record was recorded by a person not in the family (such as a census taker), then the later records may be the more accurate ones if the other person recorded erroneous information.
It is important to note that at this point in my research of Johnston families in Brant Township, I am aware of two different families: William JOHNSTON and Jane DOBSON, Thomas JOHNSTON and Ann McBRIAN. There may have been yet more Johnston families in Brant Township. Thus I am taking care to make sure that all references here to William JOHNSTON are either clearly to the husband of Jane DOBSON, so that if there is another family then I know that I am not confusing him with someone else of the same name.
1851/2 Census
The 1851/2 census of the family ( image at https://www.ancestry.com/interactive/1061/e094-e002344401/131276 ) in Brant Township, Bruce County, Canada West, shows William (age 50, thus born c1802) and Jane (46, c1806) with their youngest son Samuel (3, c1849) born in Canada and all of their other children born in Ireland: Eliza (21, c1831), David (19, c1833), William (17, c1835), Robert (15, c1837), Abraham (13, c 1839), Jane (12, c1840) and Andrew (10, c1842). Thus the family emigrated some time between c1842 and c1849.
"The History of the County of Bruce" by Norman Robertson 1906
This secondary published source is included here to address the question of where Samuel JOHNSTON was born and also when William Johnston arrived in Brant Township.
The full history is available on three web sites ( https://ia600200.us.archive.org/2/items/countybruce00robeuoft/countybruce00robeuoft.pdf AND https://archive.org/details/countybruce00robeuoft/page/n5 AND https://books.google.com/books?id=9K0OAAAAYAAJ ), and a surname index by John Weichel in 2000 is also available online ( http://www.brucecountyhistory.on.ca/history/Robertson%20Surname%20Index.pdf ).
Was Samuel JOHNSTON born in Brant Township?
The 1851/2 census shows Samuel JOHNSTON age 3 and born "Canada", with no distintcion as to where in Canada. If the 1906 Robertson history is correct, then Samuel was born elsewhere in Canada than Brant Township. Robertson notes the June 1850 birth of William's son Nathaniel JOHNSTON (in two places in the book) as the birth of the first white child in Brant Township, so that -- if Robertson is correct -- Samuel's c1849 birth was before the family arrived in Brant Township.
Here are the specific references. Note that no primary source is given to verify these statements. This is why this secondary source must not be considered to be of the same evidentiary weight as primary sources.
Page 35, footnote
"Johnston's Corners" is the name that will always be given to the corner at which Mr. Johnston located. He there, in 1854, erected a tavern, subsequently burnt down. His son Nathaniel, born June 1850, was the first white child born in Brant. Mr. Johnston's death took place September 22nd, 1870.
Page 283
The first boy baby which came to brighten the home of a pioneer of Brant came to the log shanty of William ("King") Johnston in june, 1850. This addition to the settlement was christened Nathaniel.
Page 34 - 22 May 1849 Land Allotment in Brant to William JOHNSTON
The next party of prospectors to enter Brant consisted of William JOHNSTON, Charles NELLES and James PURDY. These men followed almost immediately those already mentioned, the date when their lot were allotted to them being May 22nd, 1849. ... William Johnston spent the summer clearing the land and erecting a fair-sized shanty for his family, which he brought into the bush in the following November [1849].
Page 34, footnote 2
Johnston, in his own name and that of his sons, took up lots 4, 5 and 7, on both concessions, north and south of the Durham Road. Nelles, in like manner, took up lots 1 and 2, concession 1, S.D.R., and Purdy, lots 1 and 2, concession 1, N.D.R.
c1849 Birth of Samuel JOHNSTON
Since William JOHNSTON's family did not come to Brant Township until November 1849, it appears that Jane (DOBSON) JOHNSTON gave birth to Samuel JOHNSTON, probably in 1849, at whatever place she and the rest of the children were living before making the November 1849 move to Brant Township. This makes the June 1850 birth of Nathaniel JOHNSTON at Brant consistent as the first birth of a white child in the Township.
Appararent Death of Nathaniel JOHNSTON
If Robinson's account of Nathaniel's birth June 1850 is correct, then the infant Nathaniel JOHNSTON apparently died prior to the 1851/2 census, since he does not appear with the family in the census.
1861 Census
The 1861 census of the family not only contradicts the 1852 census for birth places. In addition, some of the ages in the 1861 cesnsus are clearly not in accord with the 1851/2 census ages, The 1861 census shows all of the children born in Canada -- all in Upper Canada except William in Lower Canada.
By 1861, some of the children had left the home. Thus there are multiple census records to locate.
William & Jane, William & Abigail, Eliza
The main family and that of son William are both on the same page ( https://www.ancestry.com/interactive/1570/4107386_00148?pid=794547623 ) and daughter Eliza's WALKER family is on the previous page ( https://www.ancestry.com/interactive/1570/4107386_00148?pid=794547623 ).
The 1861 main family consisted of William and Jane (58 & 53, born Ireland, with all children born in Upper Canada (now Ontario): David (28, thus born c 1833), M. Jane (17, c1844 vs 12 in the 1851/2 census), Andrew (13, c1848 vs 10, c1840), Samuel (11, c1850 vs 3, 1849) and Nathaniel (7, c1854). The significant differences in the children's ages from the 1851/2 census strongly indicates that the family was at least innumerate and possibly illiterate.
William & his wife Abigail are the next family, immediately after the main family. William is shown as 26 (thus c 1835 vs 17, c1835) but born in Lower Canada (now Quebec). The couple married 23 Mar 1860, wiht William stating he was 24 (thus c 1836) and born in Canada.
Eliza and her husband William Walker appear on the previous page. Eliza is shown as 25 (c 1836 vs 21, c1831) and born in Upper Canada (now Ontario).
Robert Johnston
Robert JOHNSTON's birth place changed over time more than any of the other children. The 1851/2 census shows him born in Ireland. The 1861 cenuss shows him born in Upper Canada. Later records show him born in the United States or specifically in Pennsylvania. In the 1861 census, he was recorded in Howick Township of Huron County, about 20 miles south of the family, working as a Labourer. The fact that this is the correct Robert JOHNSTON is that in addition to his name and age, the census has a column "Residence if out of Limits" which shows he resided at Walkerton, which is the town on the first concession of Brant Township just west of where William and Jane lived.
The 1861 census of Howick Township, Huron County, ( https://www.ancestry.com/interactive/1570/4391937_00088/797719727 ) shows him as a single Labourer, residing at Walkerton, born Upper Canada, Episcopalian, in the log house of William MURRY.
Abraham Johnston
Thus far, I have not found Abraham JOHNSTON in the 1861 census.  There is another Abraham JOHNSTON about 9 years older, married with 3 children, in Carrick Township of Bruce County. But this is an entirely different man. At his 2 Jan 1865 marriage in Brant Township, William & Jane's Abraham JOHNSTON shows as born in Canada West (now Ontario) and residing in Brant Township.