[ Case of John Coppinger / Proceedings of the Old Bailey ]
The Old Bailey (properly known as The Central Criminal Court of England and Wales) was the principal criminal court in London in the 18th and 19th centuries (and remains in use to this day). The records of trials held at the Old Bailey have been digitized and made freely available online (oldbaileyonline.org).
This particular case (reference number t17501017-20) was heard on 17 October 1750, making it the earliest documented reference specifically to Newfoundland dogs which I have so far found. In this particular instance, there is no actual Newfoundland dog involved in the criminal proceeding, which involved a charge of theft against one John Coppinger.
During the course of testimony, the judge asks if anyone present in the courtroom knows one of the witnesses who has spoken against John Coppinger, as some members of the jury are in doubt of her veracity.
Court. Does any person here know this woman?
John Rogers. I do, my lord. I keep the Newfoundland Dog-alehouse Charterhouse-lane.
This seems to me an important tidbit in the history of the breed, as it indicates Newfoundlands were an "established" breed (using that word loosely), one recognizable to at least some members of the general public, as early as 1750.
