This name was common among continental European royalty during the Middle Ages, and it was popularized in Britain by the German House of Hanover when they inherited the British throne in the 18th century. It was the name of characters in the novels Tom Jones (1749) by Henry Fielding and The Vicar of Wakefield (1766) by Oliver Goldsmith.
In the United States this name was only moderately common until the 1990s when it began rising in popularity, eventually becoming the most popular for girls from 2011 to 2013. A famous bearer is the Italian actress Sophia Loren (1934-).
In the New Testament Simon is the name of several characters, including the man who carried the cross for Jesus. Most importantly however it was borne by the leading apostle Simon, also known as Peter (a name given to him by Jesus).
Because of the apostle, this name has been common in the Christian world. In England it was popular during the Middle Ages, though it became more rare after the Protestant Reformation.
This name has never been common in the English-speaking world, though it has been well-used elsewhere in Europe. A famous bearer was the Italian Renaissance master Raffaello Sanzio (1483-1520), usually known simply as Raphael in English.