Francis Cosby (John Cosbie), born in 1510 and died in Ireland in 1580, became the patriarch of the family in Ireland. He was a man famed for personal courage as well as civil and military talents. When young he served in the wars of King Henry VIII _in the Low: Countries and was not distinguished. His abandonment of his native soil arose from the downfall of Sir Edward Seymour, Earl of Hertford and first Duke of Somerset, the Lord Protector of England, who had fallen into disfavor and was afterwards beheaded. His daughter, Mary Seymour, niece of Jane Seymour, third wife of King Henry VIII, married first Andrew Rogers and married secondly Henry Peycon, then married Francis Cosby. Three sons were born of the .third marriage, namely, Henry Cosby, who died in England, .Alexander Cosby, and Arnold Cosby.
After the disgrace and execution of the Duke of Somerset, in 1552, his immediate connections were excluded from and deprived of all hope of preferment. Francis Cosby with his two surviving sons by Mary Seymour, and with his second wife, Elizabeth Palmer, here in the land of his adoption (Ireland) soon found the opportunity of establishing a reputation which he had despaired of effecting in the land of his birth (England). He became an active member of the Pale against the inroads of the Irish his vigilance, zeal, and success attracting the attention of the Government. He was appointed by Queen Mary, under Her Majesty's sign manual, dated February 14, 1558, General of the Kern, a position of great trust and importance in those times.
In 1559 he represented the borough of Thomaston in Parliament, when he was constituted by Queen Elizabeth as Sheriff of the County of Kildare, being denominated in his parent, dated January 24, in the first year of Her Majesty's reign, "of Even" now "Minster Even", which place held under an old grant from the Crown, and was invested at the same time with the extraordinary and unenviable privilege of exercising martial law under his own authority solely, and of dealing out punishments, even the most penal, as he should deem meet. O'Hart, in his Irish Pedigrees, stares that "after Leix had been formed into a county the following seven families were the chief English settlers during the reigns of Queen Mary and Queen Elizabeth and were called the seven tribes, namely, Cosby, Harrington, Bowen, Rush, Harpole, Hitheringcon, and Hoveden."
General Francis Cosby fell in the battle of Glenmalure, at the head of the Kern which he valiantly led to the charge although then 70 years of age (1580).
Francis Cosby's sons by his first wife, Mary Seymour, the daughter of the Duke of Somerset, were:
1. Henry Cosby, who died in England.
2. Alexander Cosby, inheritor of the estates.
3. Arnold Cosby, who served under Robert, Earl of Leicester, with great reputation in the Low Countries (1586), with the celebrated Sir Philip Sydney. He received from Queen Elizabeth a pension of three shillings per day until he should be otherwise provided for in the army of the Kingdom.
By his second wife, Elizabeth Palmer, there was an only child,
4. Catherine Cosby, who married Archibald Moore, Esq. There were no children of this marriage.
 Henry Duke, Councilor - His Descendants And Connections: Comprising Partial Records of Many Allied Families; by Walter Garland Duke; Dietz Press, 1949 Virginia - Cosby Lineage page 296-297
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