According to "The Formans of Westchester County, New York," in 1715 Jacob Forman and his brother Isaac Forman served in the "Company of Soldiers under the Command of Capt. Samuel Dick'n at Oyster Bay." Jacob marked al his "creatures" with a crop on the near ear and a half penny on each side of the ear.

By 1722 we find that Jacob Forman was listed among the eighteen original patentees of the Town of North Castle, Westcheter County, New York. In 1722 Jacob, with Robert Carpenter and others, sent a petition from North Castle to Governor Clark, so it is presumed that Jacob was already an inhabitant there.

The Forman early belong to the Crompond Presbyterian Church, a place of worship originally built around 1738.

Jacob Forman was mentioned in the will of Nicholas Lange in 1728 as the husband of his daughter Elizabeth Lange.

Jacob Forman had married Mary Wright as his first wife, and she had died before 12 March 1720.