Henderson was on loan at the Blades from Premier League rivals United for the 2019-20 campaign.
The 23-year-old goalkeeper spent the 2018-19 season on loan at Chris Wilder’s side as well, as he helped them win automatic promotion from the Championship.
The former England Under-21 international played 36 appearances in the Premier League for United this past season, and he also played four times in the FA Cup for the Blades.
Back in the 2018-19 campaign, Henderson played 46 times in the Championship for the Blades, and actually provided one assist.
Henderson has thanked everyone at the Yorkshire club on Twitter, and he is now looking forward to what likes ahead of him, with the 23-year-old set to link up with the United first-team squad for pre-season soon.
Thank you for everything @SheffieldUnited ️ pic.twitter.com/bVAe3nKPZA
— Dean Henderson (@deanhenderson) August 19, 2020