The Phebe who married Cornelius Shaw wasn't a Joslin, she was a Cornwell, the widow of Jacob's son, John.
""JOHN JOSLIN - One of the early settlers in Fairfield Township, Cumberland County, was William Joslin. He was almost certainly from one of the towns on the eastern end of Long Island, New York, but not of the first migration of some of these people to Fairfield Township in 1697. William Joslin was born about 1701 and died August (bur. 25th) 1771, aged "about 70." He left Fairfield Township about 1730 and purchased land at the Indian Fields (East Bridgeton). At this place, he married Chrisitiana Garrison, daughter of Jacob Garrison, Jr (676-1751) who lived nearby. In 1753 Jacob Richman, a Deputy Surveyor for the West New Jersey Society, was instructed by Lewis Johnston of Perth Amboy, then agent for this London group of proprietors, to set off 220 acres of the Society's Middle Tract in Deerfield for William Joslin. The deed, however, was ordered to be made in the name of his son, Jacob Joslin. (Original surveys of the West New Jersey Society owned by the Editor) William Joslin supposedly lived on this tract with his son, Jacob*. The latter was born October 23, 1728 (Old Style) and died at Deerfield on March 27, 1797. He was twice married. His last wife was Phebe. John Joslin, of this Militia Roll, was a son of Jacob Joslin. He was born in Deerfield on August 14, 1756 and died there on January 31, 1797. His wife was Phebe Cornwell, daughter of John, who lived nearby. They had two children, viz., John, who died an infant in 1796 and Jeremiah. The latter sold out in Deerfield on April 11, 1806 and is believed to have gone "West." As late as fifty years ago, there were many descendants of William Joslin living in Cumberland County, particularly around Newport, Downe Township, but they have largely died out. There are thousands of Joslin descendants now living in other parts of the United States. "It may be of interest here to name the adjoining land owners and neighbors of William Joslin at Deerfield in 1753. North, west and south, on lands now part of the Seabrook Farms, lived Daniel Ogden, David Stratton, Thomas Nichols, Jeremiah Bennett (1st), John Robinson, Arthur Garrison and Joseph Smith. Some of these lands, or a portion of them, may still be privately owned. East and southeast lived Nathan Tarbel, William Castro (1st) and Dan Bowen, Sr.
"ISRAEL JOSLIN - was a son of Jacob Joslin mentioned in the account of Willliam Joslin."
*Jacob m. Mary Barreatt 12 Nov 1795. A record shows that on 22 July 1777 Jacob "was a witness to will of William Castro" whose "plantation" adjoined Jacob's in Deerfield, Cumberland Co. They were members of the Fairfield Church. Jacob made his will 12 Nov 1796; it was approved 29 June 1797. In his will he gave Mary all the property she owned before he married her. Jacob gave each of the first four sons -- 20 shillings; and to son Ephriam "the home plantation and the residue."; to grandson, Josiah Shaw L9 when 21 years of age. Executor, son Ephraim, witnesses were William Garrison, Joseph Smith and Susannah Shaw.
Children of Jacob and Mary born in New Jersey, but birth order not known.
1. John, b. 14 Aug 1756, Deerfield; d. 31 Jan 1797; m. Phoebe Cornwell who m. in 1797 (2) Cornelius Shaw. His children named in his will were Jeremiah, Amy and Mary.
3. Israel -- m. Demaris ___, had son Ezekiel -- ancestor of Lowell Joslin, Mrs. Mull and Larry Marshall.
5. Ephraim m. Susannah Garrison
**probable daughter would be 6. Susannah Shaw (possibly m. Abijah Shaw) mother of Josiah
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Family Tree Maker CD182 Family History: New Jersey Genealogies #1, "Genealogies of New Jersey Families", Volume 1, The Isaac Joslin Family of Downe Township,© Genealogy.com March 11, 2002. This article is from the Genealogical Magazine of New Jersey , Vol 51 (1976), pages 432-440.