He had a brother, William, for whom, in 1552, he procured a licence to trade in England as owner of a ship of 100 tons.

Even as late as 1656, there were not a dozen ships of this burden in Scotland, so William Knox must have been relatively a prosperous man.

In 1544-45, there was a William Knox, a fowler or gamekeeper to the Earl of Westmoreland, who acted as a secret agent between the Scots in English pay and their paymasters.

We much later (1559) find the Reformer's brother, William, engaged with him in a secret political mission to the Governor of Berwick; probably this William knew shy Border paths, and he may have learned them as the Lord Westmoreland's fowler in earlier years.
About John Knox's early years and education nothing is known.

He certainly acquired such Latin (satis humilis, says a German critic) as Scotland then had to teach; probably at the Burgh School of Haddington.