Turner will complete the move on Friday and join the Championship's bottom club in time for Saturday's trip to Hull.
As part of the deal, North End goalkeeper Andrew Lonergan is to train with the Toffees a couple of times a week, but will remain part of Phil Brown's squad.
Preston chairman Maurice Lindsay told the Evening Post: "Phil Brown wanted competition for Andrew Lonergan for the goalkeeper's position.
"We agreed a deal with Everton for Iain Turner and will take him on a 93-day loan.
"During the discussions with David Moyes, it was suggested that Andrew could train at Everton two or three times a week to give him some freshness. That will happen, but he won't be leaving our register and we will continue paying his salary."
Source: PA
Source: PA