His descendants in North America include Giffs in Chicago, Keays in California, Georgia and Florida, MacDonalds, Mordens and Haynes in Ontario, and Wrights and Lewis' in Alberta. For a full list of descendants I've been able to document, see the Last Name Index related to Jeremiah Giff.

The scant evidence I have of his existence is (a) a record of his marriage in 1795 to Miss McCowan in Waterford, Ireland and (b) a note written in the 1930's by my great-grandmother (Emily Wright-Mylks) saying that his wife died leaving an annuity to their young daughter Eliza and that he subsequently remarried.

In the mid-1930's Jeremiah's great granddaughter, Emily Wright-Mylks, was asked to record her memories of her mother's (Eliza Keays) family. She wrote:

"By request I will try and write the History of my mothers family as I recollect it as told to me by my mother when I was quite a small girl. I cannot give dates.

My Grandfather’s name was James Forbes Keays. He was born in Kings County Ireland. He was the second son and the law at that time was the eldest son inherited the estates. He was bought a Commission in the army⁽¹⁾ and when quite a young man came to Canada. He was appointed by the government to the Commissariat department while the Lachine canal was being built in Quebec, He was highly educated and understood French etc.

My Grandmother was born in the city of Waterford Ireland. Her name was Eliza Amelia Giff. She too was educated at a boarding school in her native city. When she was quite a young child she lost her mother. Her father married again. She was the only child of the first marriage. When she was about eighteen she came to Canada with some cousins by the name of Link. It was a new country then it taking about six weeks to cross the Atlantic.

After she was here she met my Grandfather and they were married. They first lived in Quebec at the Ile aux Noix. There was where my mother was born. Later on he was moved to Bytown which is Ottawa now where there were more public works carried on. From little souvenirs I have seen there was high life for those days.

When quite a young man 45 years of age he was stricken with Dropsy and passed away leaving my Grandmother with her little family alone in a new country. My mother aged about 10 and a son William there having lost a son between named James Forbes⁽²⁾ after his Father but my Grandmother was a strong minded woman and they had a government grant of 200⁽³⁾ acres of land situated near North Augusta. She came to the woods bringing her old servant man and his wife with her. There she made a living and faced the change of circumstances bravely.

After being a widow about five years she married Samuel Jr. Bellamy quite a wealthy man a widower with five⁽⁴⁾ children after which her troubles of getting on were at an end. The two families of children grew up together it was said a stranger would scarcely know the dividing line (of course bringing her two⁽⁵⁾ along).

It seems there was money left in the bank at Waterford by her own mother which as long as she lived there was a dividend came to her but at her death it ceased.

I remember my Grandmother quite well as I was about fourteen years of age at the time of her death. She was a very fine gentle lady. Her advantages were better than my own Mother as she grew up in a new country. William her son was quite well educated the money that came to her  every year she spent by sending him to Toronto to school his family are living in the U.S.⁽⁶⁾ The daughter⁽⁷⁾ and Mrs. Carpenter at Jamestown NY.

Emily Wright Mylks

There were two sons Reginald Horton & William.”

Notes:

1. I have since found that James Forbes Keays was never an officer in the British Army before he came to Canada. The story is apocryphal.
2. The baby James Forbes Keays, born in 1859, died in Buffalo, N.Y. in 1861. James’ and Eliza’s other son was named John Leslie Keays born 30 Jul 1823. (baptismal certificate)
3. The land they moved onto was 100 acres in Augusta that had been bought by James F. Keays in 1825. The grant was for 300 acres and was first rescinded, at James Keays’ request in 1829, then re-awarded and given posthumously as a scrip to William Jeremiah Keays in 1848.
4. Samuel Bellamy came to the marriage with six children aged 1 to 13.
5. Eliza brought 2 children to the marriage: Eliza, and William, John Leslie being the child that died. At some point Eliza’s nephew, Jeremiah Giff, who had been born in St.Kitts, West Indies in 1831, came to live with them. He grew up as a full member of this large family.
6. William settled in Buffalo, N.Y., first in 1861 and then again in 1881.
7. The daughter, Daisy Keays, married Charles Carpenter in Jamestown, New York.

These are pretty skimpy data, but upon them, I have been able to research and develop several useful historical stories: the descendants of this Jeremiah Giff's grandson, Jeremiah Giff (b. 1831), the life of William Jeremiah Keays and much of my my own family history.

Jeremiah's daughter, Eliza Amelia Giff, was born in 1797/8 in Waterford, Ireland. She was educated in "a private school" and, after her mother died and her father remarried, she emigrated to Canada in about 1815. She came to settle in Prescott, Ont. with a family (cousins?) named Link.

In 1818, she married James Forbes Keays and had 3 children: Eliza Keays, John Leslie Keays and William Jeremiah Keays. Sometime in the second quarter of the 19th century, her nephew, Jeremiah Giff came to live with her and her family in Augusta Twp. Jeremiah Giff, grandson of Eliza's father, was born in St, Kitts, West Indies in 1831.

Grandson Jeremiah Giff and his 1st cousin William Keays were contemporaries and fast friends. When William moved to Goderich, Ont., Jeremiah followed. When William left Goderich to emigrate to the U.S., so did Jeremiah. Both went to the U.S. to take advantage of the growth of the railroads - William to Buffalo, N.Y., Jeremiah to Chicago, Ill.

Today, descendants of Jeremiah Giff (b. 1831) live in Chicago, Ill. Descendants of William Keays live in California, Georgia and Florida and descendants of Eliza Keays (including me) live in Ontario and Alberta.

You can see the "Descendants of Jeremiah Giff"  here. There is a full surname index and a complete listing of all 284 descendants I've found. You can also download the gedcom file of his descendants.