The landscape of Passaic County, near the north edge of New Jersey, spans some hilly areas and has dozens of lakes. The county covers a region about 30 × 20 miles wide (48 × 32 km). The region is split by major roads, including portions of Interstate 287 and Interstate 80, near Paterson.

Passaic County is shaped like a bent hourglass with the area above the neck running generally north and south and the portion below, east to west. The upper half of Passaic County is characterized by large lakes and watershed areas with low-density development.