Brannan is a surname of Irish origin, derived from the Gaelic 'O'Braonáin', which means 'descendant of Brannoc'. This name was popularized by the town of Brannenstown in County Dublin, Ireland. It's also associated with the San Francisco neighborhood known as 'Brannan Heights', named after William Brannand who subdivided and sold land there in the mid-19th century. The name Brannan is rare, but its Irish heritage and California history make it unique.
"The name Brannan saw a gap of 16 years between its peak years for birth registrations, with 6 babies named Brannan born in 1979 and 5 in 1995, making a combined total of 11 children."