Palace secure Liverpool, Chelsea target Williams to long-term deal
"It feels great to have signed a five-year deal with the club I've grown up playing for. Palace is a major part of my life," he told the club's official website.
"I've had a really good season, I never expected to play 18 games, score one goal and have six assists.
"I've had time to get stronger physically and psychologically as well since I've been injured.
"I've had great support from the fans, my family, the staff and the players. I'm looking forward to next season now."