—In an action for a judgment declaring Local Laws, 1991, No. 8 of the County of Westchester unconstitutional, the plaintiffs appeal from an order and judgment (one paper) of the Supreme Court, Westchester County (Donovan, J.), entered June 19, 1992, which is in favor of the defendants and against them.
Ordered that the order and judgment is reversed, on the law, without costs or disbursements, it is declared that Local Laws, 1991, No. 8 of the County of Westchester is unconstitutional, and the case is remitted to the Supreme Court, Westchester County, for further proceedings consistent herewith.
By its own admission, and without elaborating on the procedure employed, the County of Westchester estimated the populations of certain Federal census block segments in setting the legislative district boundaries created by Local Laws, 1991, No. 8 of the County of Westchester. Because the County’s population figures were not based on Federal census figures, but were based on the County’s base estimates, the resulting reapportionment plan is constitutionally defective *500(see, Seaman v Fedourich, 16 NY2d 94, 104; Honig v Rensselaer County Legislature, 37 AD2d 658, affd 29 NY2d 630; Thayer v Garraghan, 28 AD2d 584; cf., Thayer v Garraghan, 29 AD2d 825, affd 21 NY2d 881).
The case is remitted to the Supreme Court and the County is directed to promptly return with a plan for reapportionment based upon Federal census figures. Thompson, J. P., Bracken, Sullivan and Balletta, JJ., concur.