The club have been in discussions with the out-of-contract pair regarding new deals, but talks have been put on hold, the Millers have confirmed.
Meanwhile, Taylor has used his Instagram account to reveal that he is to move onto pastures new.
Addressing supporters, he Liverpool-born player, a £500,000 club record signing from Peterborough United in August 2016, said: "Thanks very much for the last three years. I have loved every minute of it and made friends for life.
"I have had memories that I will never ever forget and there is a lot of people to thank for that.
"I did tell the manager and staff before the last game of the season that I would rather shake hands and say thanks now than do it over the phone in a few months time or to keep conversations going to think I was leading anyone on. Because that would not have been fair.
"I know it has only just been announced, but once again thank you for letting me be a Miller and I will still love the club because it has been the best three years of my life being part of this great club and off the pitch."
Meanwhile, Barker has revealed that the Millers remain in talks with the club's two other out-of-contract wingers Anthony Forde and Joe Newell, with a decision expected in the coming days.
Newell is a target of the Millers' near-neighbours Doncaster Rovers.
Barker said: “With Joe Newell and Anthony Forde, we have spoken to them again recently and further offers have been put to them. We are expecting an answer from them one way or another shortly.”
On the situation with Williams and Taylor, assistant manager Richie Barker added: "We have spoken with Ryan and Jon but it is at a stage now where there is nothing further planned in terms of discussions.
"That's not to say we have closed the door on them. We have made some good offers to both, which still stand, but at the moment it appears that they are exploring options elsewhere, which is their prerogative and we understand that.
“That said, they haven't signed for anyone yet, and in football you never say never. It may be that they have interest from the Championship, and if that is the case then it is hard to keep hold of them. We cannot wait forever, and we have explored other options, but like I said earlier the door remains open at this stage.”