This most interesting surname is the Anglicized form of the Gaelic-Irish name "Mag Leannain", which is composed of the elements "Mag", which is the same as the Gaelic prefix "mac", son of, and a Gaelic personal name Leannain, containing the Gaelic element "leann", cloak. The name is also the Anglicization of the Gaelic "Mac Giolla Fhianain", the son of the servant of Fhianain, also Anglicized as "Gillinan"; the sept belongs mainly to the Ui Maine regions of mid-Galway and south Roscommon. The name Glennon is chiefly found in the Leinster counties, especially Westmeath, Leix and Offaly, where it is quite numerous. Dorothy, daughter of Thomas and Ann Glennon was christened on June 25th, 1770 at St. Nicholas Within, in Dublin, while in London one Hannah, daughter of Edward and May Glennon was christened on April 5th, 1785 at St. Andrew's Church, Holborn. James and Betty Glennon, Irish Famine immigrants, aged 21 and 20 respectively, sailed on the ship "Jane" from Liverpool for New York on June 4th 1847; Patrick Glennon, aged 26 yrs, and a labourer was also a Famine immigrant who sailed for New York aboard the "Atlas" from London on May 17th 1847. The first recorded spelling of the family name is shown to be that of Thomas Glenan, which was dated January 18th, 1656, marriage to Frances Foord at St. Michan, Dublin, Ireland, during the reign of Oliver Cromwell, known as "The Great Protector", 1649-1658. Surnames became necessary when governments introduced personal taxation. In England this was known as Poll Tax. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.