Sunderland have confirmed the 21-year-old’s arrival following his departure from Hartlepool United in the summer.
The full-back made over 50 senior appearances in all competitions and has now signed a two-year deal on Wearside.
Richardson will strengthen a group weakened by the departure Bali Mumba to Norwich City earlier this week.
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The Black Cats have a number of trialists seeking to impress as they rebuild from a difficult campaign in which they failed to win a league game.
There was also interest in Richardson’s former Hartlepool team-mate Josh Hawkes, but that deal is unlikely with compensation due to his former club should he opt to move elsewhere.
Dickman said: “We’re very pleased with the signing of Kenton. He has a lot of experience at National League level despite his young age, so that’s going to add something to our group and really help the younger players.
"His attitude is very good and it’s down to him now to progress to the first team.”
Richardson, meanwhile, revealed his Sunderland connection that makes the move all the more special.
“I’m delighted to sign for the club,” he said.
“It’s extra special for me because I used to have a season ticket here with my dad. I can’t wait to get going now and push on this season.”