There was Toland, of course, but given he describes himself as a deist at one point and a pantheist at another, it is not entirely clear that he was an atheist as we understand the term.
However in 1730, Wetenhall Wilkes published a book in Belfast called An Essay on the Existence of God, particularly in answer to Two Atheistic Letters of Mr. I— T— dated from Dublin 1729. As described, JT is unquestionably an atheist. To put the date into context, the man commonly acknowledged as the first atheist to openly deny the existence of gods was Jean Meslier, whose writings were only circulated (mostly in extracts and clandestinely) after his death in 17291.
According to Wilkes, J—h T—r wrote two letters to him dated 13th December 1728 and 3rd May 1729. In the extracts Wilkes quotes, Mr JT outlines his materialistic philosophy. Wilkes also mentions a meeting in which JT and others defended their views to a sympathetic group.
JT’s arguments suggest wide reading in philosophy. In his argument as given by Wilkes the only philosopher he cites by name is Hobbes. However he also seems to draw on Spinoza’s Ethics (Chapter I, see propositions II and II) when he argues that God could not have produced the material world since nothing can confer a quality on another it does not itself possess. The assertion that motion is an ‘internal property’ of matter was also put forward by John Toland in his Letters to Serena and may have its source there 2.