Worth mentioning for the record — Loncon 3 hit 8,518 total memberships at the end of June. That’s the most members any Worldcon has ever had — surpassing L.A.con II’s 30-year-old mark of 8,365.
At that time London had 5,457 attending and 2,768 supporting members. So it has a very good shot at setting a new attendance record for a Worldcon held outside North America. Glasgow’s 1995 Worldcon currently holds that title, where 4,173 were counted present.
L.A.con II has the overall record: 8,365 was also report as its attendance figure. You can wonder — like, what about no shows? — but it hasn’t been controversial because few Worldcons have come anywhere near drawing that number.