Cross Brook is a tributary of Six Mile Run in Somerset and Middlesex Counties, New Jersey in the United States.
The source of Cross Brook is near Suydam Road in eastern Franklin Park, at . It flows through the Six Mile Run Reservoir Site and crosses Jacques Lane. After Jacques Lane it drains into the Six Mile Run at .
Cross Brook is a slow-moving stream, although it is not marshy. Some species of fish may be expected to be found in it.
The Cross Brook starts as a lake which drains into grasslands, forming a marshy area around its source. It is still muddy farther downstream. It tends to be a wide, slow, deep stream.
Cross Brook is a short stream, only crossing one road. There are a few trails in the woods that lead to it.