It is the first time that Williams has been loaned out by the top-flight side, as Ronald Koeman wants the midfielder to gain more first-team experience - which he is unlikely to get if he stayed at Goodison Park.
A player with a lot of potential
Williams is not the first youngster to arrive at Oakwell on loan from a Premier League side this summer. Chelsea striker Ike Ugbo also joined the Reds on a season-long loan and they are both seen as players with a lot of potential.
With the pair both arriving from the first division on loan, they can almost share the experience together which could help ease them into their new surroundings easier and deal with the demands that Championship football brings.
He has spent his whole career at Goodison Park, but is yet to make an appearance for the first team. However, he has been very successful for their youth teams.
He has captained the Under 23 side on numerous occasions and has impressed when he has done so. He has been on Heckingbottom's radar for a significant amount of time and he has now decided to see what the youngster can do in the second tier.
The 20-year-old will be looking to use this loan move as a springboard for his career, as at his age it is approaching the 'make or break' time in regards to whether he will ever make it at Everton.
However, even if he does not impress enough to earn a spot in Koeman's starting line-up next season, he could still be an asset to any Championship side if he proves his worth.
Heckingbottom delighted to sign 'all-round' midfielder
Williams has been described as a very versatile midfielder, who can fill a variety of different positions. This is very useful for any Championship manager due to the demands of the league resulting in many suspensions and injuries. Heckingbottom stated this was one of many factors which persuaded him to bring Williams to the club.
He told Barnsley's official site: “We have been looking at Joe for a while and have been to see him play a few times. We have had success in player recruitment from Everton in recent times so I have to thank them for continuing to trust us with that."
He added: "Joe will be a different type of player to what we have at the Club, as he has all the attributes and ability to be considered an all-round midfielder. We’re looking forward to him getting going and it’s important for him to now get some games in the remaining friendlies we have.”
Williams has become the latest of a long list of players who have already arrived at Oakwell this summer. The likes of Zeki Fryers, Lloyd Isgrove, Liam Lindsay, Jason McCarthy, Cameron McGeehan, Ethan Pinnock and Ugbo have all already arrived at the club.
The midfielder feels that the Championship is the ideal environment for him to improve his overall game. He said: "The Championship is fast, it's frantic, played at a high-tempo. I spoke with Gethin [Jones] who was here last season about it and he told me the atmosphere is electric and everything is so fast. I think the division should suit my game."
He continued: "Everybody I've asked has had great words for Barnsley, they couldn't speak any more highly of the Club and I've been really impressed myself since I've got here. I've met the gaffer and he's explained his plans for me and I feel he's the perfect manager to bring me on as a player, to develop my game."