The 19-year-old, who has spent two previous loan spells at Ewood Park, was a regular during the run-in last season.
"With the new manager coming in, we were waiting to see if Todd was going to be part of his plans, but they see the advantage of him coming out and playing in the Championship again for a full season," manager Gary Bowyer told the Lancashire Telegraph.
"Todd kicked on massively when he came and joined us last time. On the back of his performances here, he earned himself a new contract at Chelsea and rightly so. We'll be looking for him to come and make the same impact as he did last season."
The defender, who also had a spell on loan to Preston, signed a new deal with the Blues in April to keep him at Stamford Bridge until 2016.
Blackburn last week