A noted coffee-house in Change Alley, described in the Tatler as the general mart of stock-jobbers.
What is now called the Stock Exchange was called Jonathan's.
“Yesterday the brokers and others ... came to a resolution that [the new building] instead of being called `New Jonathan's,' should be called `The Stock Exchange.' ... The brokers then collected sixpence each, and christened the house with punch.” —Newspaper paragraph (July 15, 1773).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894