Peter, The given name Philadelphia didn't entirely die out in the 20th century, but like any first names it's usage changed over the years. If you go back far enough there are plenty of other female names that have also fallen out of fashion - like Gresilda, Godlefe or Parnell. What is true is that Philadelphia was much more common between say 1600 - 1900, and particularly in the South (London, Sussex and Kent especially). Even so, if you look specifically at the 18th century, names such as Frances, Harriet, Caroline and Amelia were more frequently found than Philadelphia and others such as Gertrude and Constance were almost as popular back then. Duncan, Dundee