It rounded off a record-breaking summer.
Despite the cyberattack targeting Collins Aerospace IT, which impacted airline systems at Heathrow and other airports in Europe, it was still a milestone month for passenger traffic.
Heathrow said it continued to the most connected airport in the world for the third consecutive year.
Security performance was consistent, with 95% of passengers waiting less than five minutes in security screening lines.
Management said Heathrow helped drive over £215 billion in trade last year, connecting businesses to global markets.
Heathrow CEO Thomas Woldbye said: “This summer at Heathrow was one to be celebrated. Operating Europe’s largest airport doesn’t come without its challenges, but I’m proud that our team delivered under pressure “
“We welcoming nearly 7.4 million passengers in September alone while maintaining strong performance in punctuality and security and we continued to lead the pack in global connectivity