Three golds went to Jason Djaffarsah, for his 50m and 100m breastrokes, and 200m freestyle.
Two went to Sam Preece, for his 100m backstroke and 50m butterfly, and Grace Kyle won gold in 50m breaststroke.
Head coach George Brown said he was excited by the results his 15 competitors, who represented more than half of the club, had delivered.
‘Thornlie’s team was one of the largest participating groups from probably the smallest club in attendance,’ he said.
‘Thornlie outshone their competitors and dominated the event from the outset.’
The club is now preparing for the Swimming WA junior state championships this month and the Age Group and Open States in October.