Some names shock parents when they realize just how popular they are (for example, Jayden). Other names shock parents when they realize how relatively uncommon they are. Jack is a common name for US boys, but few parents know the name Jackson is much more popular (in 2010, Jackson was the 25th most popular name for American boys, while Jack was down at 44).
The name Jack originally derived as a nickname from the name John (which in 2010 was also less popular than Jackson), and was often used to refer to an Everyman, until it independently became an established given name.
Although the name sounds very popular, it has never been an American Top 10 name, and the closest it's been was in 1930, when it reached number 14. It has been mostly (and very slowly) declining in popularity ever since.
