Callen Gill, who goes to Bitterley C Of E Primary School in Ludlow, began his swimming challenge after overhearing his mother on the phone with a friend.
Mum, Amy Gill, said: "I was on a Teams meeting with a friend of mine who happens to be the chair of Ludlow Swimming Club.
"We were talking about how we could raise money and Callen said 'I would like to do something'."
Amy, who describes her son as a "water baby" due to his love of swimming, asked what he had in mind.
"He first thought about swimming the length of the Channel, but then settled on 26 miles - marathon distance," she said.
She added that Callen had only planned to raise £300, but after setting up a JustGiving page, his swimming feat managed to pull in more than £1,000.
"I am very, very proud of him," said Amy. "He began his swimming marathon at the beginning of August and did a mile a day.
"He had planned to finish in three weeks, but he finally did his last mile on August 31. In total he did 18 swims in 29 days. That's a whopping 1,664 lengths!"
The money, which is still coming in as Callen's JustGiving page is still active, will go towards new resources for Ludlow Swimming club, said Amy.
Anybody who wants to donate to Callen's swim can do so at justgiving.com/crowdfunding/amy-gill-1