In November 1823, the southern portion of Sussex County was set off as a separate county known as Warren County. The northern portions of Hardwick and Independence Township, which remained in Sussex County, became Green Township on December 27, 1824.

In 1829 part of Green Township became Byram Township, but in 1853 Green Township was expanded to include a section of the old Newton Township. In 1904 a portion of Green became Fredon Township. In 1881, the area was listed as 19.65 square miles; and today Green encompasses 16.5 square miles.

The township was named after Ephraim Green, who settled near Greendell in 1770. Many sections of Green retain their identity as Tranquility, Huntsville, Greendell, and Yellow Frame.