The left-back, 19, has played in three games for the Seasiders after agreeing terms to an initial month-long stay in November.
With Paul Ince's squad particularly light on numbers this weekend due to three suspensions and fellow defender Craig Cathcart doubtful for the Derby clash due to a knee injury, Blackett's arrival will boost Blackpool's numbers.
"The kid has done well," Ince told the club's official website.
"He's only 19 but I think the last game and the game before he grew into his role.
"I think he'll only get better. He's better off playing in this environment and learning his trade."