Anna, who learned to swim with Chorley Marlins, also claimed a world record as she and her three team-mates - Adam Peaty, Kathleen Dawson and James Guy - stormed to a sensational victory in the mixed 4x100 metres medley, shaving 0.83 of a second off the previous best set by China last year.
Commons Speaker Sir Lindsay watched the thrilling race on TV and said: "Anna was absolutely brilliant - they all were. I was watching and I couldn't believe how far ahead she was.
"It was a case of Chorley shines through again on the world stage.
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"Isn't it fantastic that someone who comes from Chorley and came through Chorley Marlins Swimming Club could be standing on the podium with a gold medal around her neck?
"I just want to say to Anna: 'Thank you for putting Chorley on the world stage. You did the town proud.'"
Anna joined Chorley Marlins at the age of eight. Head coach Mary Parkinson, who coached her for four years, said: "We're all so proud of her. She is an inspiration to all the youngsters at our club.
"It's every swimmer's dream to go to the Olympics, but to win a gold medal is absolutely amazing.
"When Anna came to us as an eight-year-old you could see she had a real talent. In her first year she was swimming against nine-year-olds and by the age of 10 we were putting her in against swimmers who were 12.
"She stopped swimming for four years, but thankfully came back to the sport.
"To do a 52 (seconds) in today's final was amazing swimming by her. She has such maturity. She knows what she wants and knows exactly how to swim a race.
"She was up against Caeleb Dressel (men's 100-metres freestyle champion) in the final leg, yet it didn't affect her. She was focused on what she had to do and did it. Her finish was amazing. She's not very tall, so to have that power and strength is unbelievable.
"There's a lot more to come from Anna. Everyone will be keeping an eye on her now and rightly so. She is a real credit to Chorley."
Anna's old school, Withnell Fold Primary, tweeted: "What a fantastic achievement. A gold medal and a new world record. Well done to our past pupil Anna Hopkin - we look forward to welcoming you back into school in person, with your medal."
And Inspire Youth Zone in Chorley wrote: "Huge congratulations to Chorley's Anna Hopkin on your Olympic gold medal,. We're all so proud of you. Hope you can come and show our young people your medal when safely back in the UK."