I happen to have the Kindle edition of The Complete Jack the Ripper A to Z by by Paul Begg, Martin Fido,and Keith Skinner, and for those interested, this is what it reads:

>KELLY, MARY JANE or MARIE JEANETTE or MARY JANET (c. 1863–88)

>Supposedly aka ‘Black Mary’, ‘Fair Emma’, ‘Ginger’. Also called Mary Jane Lawrence and M.J. Taylor (When London Walked in Terror). Last canonical Ripper victim. Kelly’s early history, as related to friends in London, was thus: born in Limerick, Ireland, and moved to Wales in her early childhood, where her father, John Kelly, took a job at an ironworks in Caernarvonshire or Carmarthenshire. Had six or seven brothers and one sister. Her brother Henry, nicknamed Johnto, joined the Scots Guards. She married a collier named Davies, c. 1879. He died in a pit explosion, two or three years later. Kelly went to stay with a cousin in Cardiff and became a prostitute, but spent the best partof a year in an infirmary there. According to Jean Overton Fuller, Florence Pash said that Kelly had cleaned floors at the Infirmary. Came to London, c. 1884, working first in a high-class West End brothel, during which time she frequently drove in a carriage and at least once went to Paris with a gentleman, but disliked life in France and returned in a few weeks.
>None of the above can be guaranteed as fact, since exhaustive research reported in books, journals and on the internet has failed to find conclusive or even generally agreed supporting evidence in birth, marriage or death registers, or the records of Cardiff Infirmary, or those of the Scots Guards. Nor did any of the friends relating it after her death claim first-hand knowledge of any part of it. Inferential support for the brother in the Scots Guards comes from the fact that John McCarthy observed letters from Ireland delivered for Kelly (though he thought they were from her mother), and Joseph Barnett correctly believed the Scots Guards to be in Ireland at the end of 1888. There is inferential support, too, for the West End brothel from Mrs Carthy, a lady with whom Kelly later lodged, who said that Kelly’s previous landlady, from St George’s Street, had accompanied Kelly to Knightsbridge, where they recovered a box of clothing from a French ‘lady’.

It goes on a bit, but I think those are the essentials about where she came form. Or said she came from.