Declan is a name that dates all the way back to the 5th century. It's the English version of the Irish name Déaglán and is believed to mean "man of prayer" or "full of goodness."
The most notable Declan was an Irish missionary and preacher, Saint Declan, also known as Declan of Ardmore. He lived during the 5th century and is known for converting a large population of people to Christianity in the Irish kingdom of Déisi Muman. St. Declan's Stone is a tourist attraction in Ardmore, Ireland (where Declan founded a monastery), and has purportedly been the site of many miracles.
Declan is the most common spelling, though Declyn is gaining traction, especially as a girl's name, and Declann, Declin, and Declynn have also been used.
While Declan has long been a favorite across the pond in Ireland, it didn't start gaining notice in the United States until 1998, when it first made the Social Security Administration's list of the top 1,000 boys' names. It's steadily climbed through the rankings ever since, breaking into the top 100 names in 2019.
Declan is one of the many Irish names that has captured American parents' attention in the past decade or so. Along with Declan, names like Aiden, Arlo, and Rowan have been making strides in the U.S. If this trend continues, expect to see Declan in the charts for years to come.
Declan of Ardmore : Christian religious figure in ancient Ireland
Declan O'Brien : Director known for the horror film series Wrong Turn
Declan Costello : Former attorney general of Ireland
Declan MacManus : British musician better known by his stage name Elvis Costello
Declan McKenna : British singer, songwriter, and musician