Frederick Joseph Jennings was the third son of Daniel Corley Jennings and Johanna Bray. He was born in Tuam, County Galway, where his father Daniel was a sub-inspector in the R.I C., and baptised in Tuam Cathedral. His baptismal sponsors were Andrew John Jennings and Ellen Bray. Andrew Jennings was his uncle. Ellen Bray was his maternal aunt.
Frederick J Jennings went to school with his brothers at Tramore Boarding School. He appears to have been baptismal sponsor for his younger brother John Bray Jennings, although he would have only been five years older at the time.
He died in the Richmond District Lunatic Asylum on 12th November 1911 at the age of 62, and is buried in Glasnevin Cemetery. It was noted that he had been a medical student and was from County Clare.
 Baptisms Tuam Cathedral 1845- NLI Pos 4222