It has been in use as a feminine given name in the English-speaking world since the 1920s, possibly inspired by the heroine in the serial novel The Skyrocket (1925) by Adela Rogers St. Johns [1]. As a Hebrew name it is unisex.
In England, Sarah came into use after the Protestant Reformation. It was consistently popular in the 20th century throughout the English-speaking world, reaching the top of the charts for England and Wales in the 1970s and 80s.
Notable bearers include Sarah Churchill (1660-1744), an influential British duchess and a close friend of Queen Anne, and the French actress Sarah Bernhardt (1844-1923).
As an English name, Monica has been in general use since the 18th century. In America it reached the height of its popularity in the 1970s, declining since then. A famous bearer was the Yugoslavian tennis player Monica Seles (1973-).
In the English-speaking world this name has been occasionally given since the early 20th century. It started rising in America after the variant Lorelai was used for the main character (and her daughter, nicknamed Rory) on the television series Gilmore Girls (2000-2007).