Dey Mansion is at 199 Totowa Rd. in Preakness Valley Park. The Georgian manor was built by Dirck Dey, a Dutch-born planter, in the 1740s. His son Theunis, commander of the Bergen County militia, invited Gen. George Washington to use the mansion as his headquarters in 1780. The stately house is furnished in period. On the 2-acre site are a blacksmith shop, a plantation house, a formal garden and a family cemetery.