Which British Prime Minister listed had an American-born mother?

Sir Winston Churchill's mother, Lady Randolph Churchill, nèe Jennie Jerome, was an American-born British socialite, who was born on January 9, 1854, in the Cobble Hill section of Brooklyn, New York. She met Lord Randolph Churchill, at a sailing regatta, and they were married on April 15, 1874. Sir Winston was born on November 30, 1874.

According to his biographer William Manchester, Winston was most likely conceived before the marriage, rather than born prematurely. A recent biography has stated that he was born two months prematurely after Lady Randolph "had a fall.". When asked about the circumstances of his birth, Winston Churchill would reply, "Although present on the occasion, I have no clear recollection of the events leading up to it."

This information might be interesting for you:

Sir Winston was Prime Minister from 10 May 1940 – 26 July 1945 and again from 26 October 1951 – 6 April 1955.

Lady Randolph Churchill died on June 29, 1921, from a hemorrhage. She was 67. Her resting place is St. Martin's Church, in Bladon, England

Sir Winston Churchill wasn't the only British Prime Minster to have had an American-born mother. Harold Macmillan's mother, Helen (Nellie) Artie Tarleton Belles, was also an American. She was an artist and socialite from Spencer, Indiana.