Early Life
A Henry Slack was baptised 28 July 1721 at Hesket-in-The-Forest, Cumberland. Given that Henry married in 1751, this seems like a high probability match for the correct baptismal record, though unfortunately there are no parents recorded.
Ancestry trees have his parents Joseph George Slack and Mary Stephenson, though it's not clear on what basis.
If we look for other Slack children baptised at Hesket at roughly the same time we find a Margaret Slack (31 Aug 1729) whose father is given as Thomas Slack. In turn, a Thomas Slack married Grace Scott on the 7 Aug 1720 in Hesket in the Forest. Given that Henry Slack's daughter was called Grace, I'm taking this as strong evidence for a correct relationship.
However one of the children that I am attributing to Thomas and Grace Scott is Thomas Slack, born 1723 (possibly
https://www.findagrave.com/memorial/93582285/thomas-slack). His baptismal record gives no parents and I note that in other places, this Thomas Slack is made the son of Joseph Slack and Mary Stephenson (e.g.
here). BUUUT, this famous Thomas Slack could instead have been born in July 1723 and baptised at St Mary in Carlisle, son of Isaac Slack.
So my conclusion is that the "famous" Thomas Slack was born in July 1723 at Carlisle, whereas
this Thomas Slack was born in December 1723 at Hesket-in-The-Forest, to Thomas Slack and Grace Scott.
Family Life
A Henry Slack married Sarah Railton at St Cuthbert on the 18
th April 1751. This seems the most likely match, given the age range and location. Also note that Henry's grandmother was Ann Railton, presumably of the same family.
Death
We have a couple of possible dates of death:
- Henry Slack died in 1773 and was buried on the 12th of September 1773 at Hesket-in-the-Forest1.
- Henry Slack buried 8th October 1808 in Carlisle2.
I think the former is more likely, based on location, but we can't be certain. Of note and contradicting this is the fact that Henry's wife Sarah died in 1784, and in her burial record her husband's name is mentioned, which possibly suggests that he was still alive in 1784.
Footnotes
[1]
https://www.familysearch.org/ark:/61903/1:1:J89G-6M3
[2]
https://www.familysearch.org/ark:/61903/1:1:J89G-X6G