Old St. Paul's is a novel by William Harrison Ainsworth serially published in 1841. It is a historical romance that describes the events of the Great Plague of London and the Great Fire of London. In 1840, Ainsworth published Guy Fawkes and The Tower of London. When their serial publications were completed at the end of the year, Ainsworth began writing Old St. Paul's, A Tale of the Plague and the Fire. Ainsworth, in a letter to James Crossley 7 December 1840, wrote: "You told me that you have a second part of De Foe's History of the Plague. Pray bring this with you. I will take the greatest care of it, but it is quite necessary I should see it, as I commence a new Romance with the New Year, under the title of The Plague of London. If you have any other tract relating to the period, or to the Fire, I shall feel obliged by the loan of it." Old St. Paul's ran in The Sunday Times from 3 January 1841 to 26 December 1841, and he was one of the first writers to appear in a national paper in such a form. Ainsworth was paid 1,000 for the work with control of the copyright. The work was later illustrated when it was published in a three volume set by Cunningham.