My 4th Gt-Gr mother Anna Margaretha Plack (c1756-1813) married Johannes Weygand (1750-1797) around 1777. They and their Wiegand descendants lived in Eifa, Hessen-Darmstadt, Germany. My GtGt Gr father, Johann Jost Wiegand (1808-1890), came with family to the US in 1861 and settled in Connecticut.
I have nothing further on the Placks but their records are probably in the Biedenkopf church records [as were the Wiegand's].