The biggest trees in Hackensack are the Cottonwoods in several city parks, notably Foschini and Columbus. However, this is a very fast-growing species and probably even the biggest are no more than 150 years old. Find some of the slow-growing Beech in Borg's Woods, and those are probably the oldest in the city. They are not the largest trees in Borg's, there are fast-growing Tuliptrees and Red Oaks that are larger. Red Oak is not known for being fast-growing, but sometimes they do. Pin Oak is also very fast-growing, a prime example on the lawn at First and Central Ave. The Beech in Borg's are probably the oldest trees in Hackensack and anywhere in Bergen County. The woods was documented as 200 years on in 1977, but individual trees are far older. Could some be 300, 400, or even 500 years old. I wouldn't doubt it.