He will take over the reins from Nigel Wedgwood, who recently stepped down from the role.
Mr Williams arrived at Eslaforde park as Mr Wedgwood’s vice-chairman last summer, with the two having previously worked together at Grantham Town.
"We are delighted to announce that Dean Williams will be staying with us as chairman,” a club statement read.
"Since Nigel’s departure, Dean has been leading a restructure of the board and has initiated a consortium of investment that will help support and safeguard our club alongside our ambitions."
Mr Williams said he and his wife Roz were delighted to be staying on board with the Greens.
"Sleaford Town is a great club and that means a great community,” he wrote on social media.
"It’s been a huge part of my life (and Roz’s) over the last 12 months - I very much feel like an adopted Sleafordian!
“I’ve been touched by the support for me to step up as chair and build on the foundations led by Nigel.
"We remain extremely ambitious alongside our blueprint.
"We want to create history at Sleaford. I’m looking forward to playing my part in making this happen.”
Messrs Wedgwood and Williams linked up with Town before the start of last season, with club legends Brian Rowland and Jamie Shaw joining them on the board.
Last season saw the side finish 12th in the United Counties League Premier Division North, followed by a healthy home crowd.
The Greens held their end of season awards at the weekend.
Defender Mitch Griffiths got the nod from the terraces as he was named Fans’ Player of the Year.
The dressing room went for Ryan Rushen, who collected his Players’ Player of the Year accolade.
Boss Tom ward named Joe Smith managers’ Player of the Year while Kyle Watkins took home the Young Player of the Year trophy.
Sports therapist Sian Lee has left the club to join Grantham Town on a full-time basis.
“Thank you so much for keeping us safe and well,” a club statement read.