Short answers, pulled from the story.
The title "justice of the peace" dates from 1361, in the reign of Edward III of England. The role itself is older: Richard I commissioned certain knights to keep the peace in 1195, and the Justice of the Peace Act 1327 referred to "good and lawful men" appointed in every county to "guard the peace."
Ada Summers, the Mayor of Stalybridge, was the first woman to hold the office of justice of the peace in the United Kingdom, qualifying by virtue of her mayoral role in 1919. In October 1920, she was appointed a JP in her own right, alongside Edith Sutton and Miriam Lightowler OBE in Halifax.
Emily Murphy of Edmonton, Alberta, was sworn in as a police magistrate in the Women's Court of the City of Edmonton on the 19th of June 1916. She preceded Ada Summers of the United Kingdom by more than three years, and Canada's appointment was the second such appointment of a woman as a magistrate in the British Empire, after South Australia.
In North v. Russell (1976), the Supreme Court of the United States held that trial before a non-lawyer judge did not violate due process, provided the defendant had the right to a full trial de novo before a law-trained judge. Two years earlier, in Gordon v. Justice Court (1974), the Supreme Court of California had held that due process was violated when a non-attorney judge presided over a criminal trial that could result in imprisonment, unless that right was waived.
Magistrates' courts handle over 95% of criminal cases in England, Wales, and Northern Ireland. All criminal cases begin in the magistrates' court, even the most serious, before more serious matters are committed to the Crown Court.
In both Hong Kong and Singapore, JPs no longer perform judicial functions. Hong Kong replaced the judicial role with full-time legally qualified magistrates, and JPs now serve as honorary titles whose duties include visiting prisons, psychiatric hospitals, and detention centres, and monitoring the Mark Six lottery draw. Singapore appoints JPs by the President under the State Courts Act 1970 for renewable five-year terms, drawing from community and professional leaders, with no judicial role.