I think of Cullen as a typical Irish-American surname, with our ancestors emigrating during the potato famine in the 1840s and until the early 1900s, settling in the northeast/midwest, ending up in big cities even if that's not the first place they came to in America.
But I think there might be earlier Cullens in America, maybe from Ireland maybe from England, probably Protestant.
Probably one of the most famous people named Cullen wasn't really a Cullen:
Countee Cullen was very secretive about his life. According to different sources, he was born in Louisville, Kentucy or Baltimore, Md. Cullen was possibly abandoned by his mother, and reared by a woman named Mrs. Porter, who was probably his paternal grandmother. Cullen once said that he was born in New York City - perhaps he did not mean it literally. Porter brought young Countee to Harlem when he was nine. She died in 1918. At the age of 15, Cullen was adopted unofficially by the Reverend F.A. Cullen, minister of Salem M.E. Church, one of the largest congregations of Harlem. Later Reverend Cullen became the head of the Harlem chapter of NAACP. His real mother did not contact him until he became famous in the 1920s.
But Rev. F.A. Cullen seems to be an illustrious African-American Cullen. Where was he from?