Hi All,
Been quite a while since I first joined this search, but it still interests me now. The first Smollet born in East Lothian was Smollet Cochran, daughter to John Cochran and Margaret Henderson on 16 March 1794 in Dunbar, this would be baptism date probably. So the Henderson line is prominent.
The earliest Smollet in Scotland, by ScotlandPeople and LDS Family Search websites is Smollet McEchny, daughter to James McEchny and Elizabeth Carns, christened on 16th October, 1730 in Bonhill in Dunbartonshire.
Hope these help.
Tom Buchanan