Many of the characters in Boromir's immediate family appear nowhere outside The History of Middle-earth, and apart from his father Boron and his son Bregor, this genealogy is provisional. Boromir's daughter Andreth is the subject of a lengthy, though non-canonical, account of her own. See her entry in the Excyclopedia for more information.
The son of Boron of the House of Bëor, and thus a great-grandson of Bëor the Old, one of the first generation of Men to cross into Beleriand. Boromir was granted the lordship of the land of Ladros, a highland country to the east of Dorthonion. We have no detailed history of his life there, but it is known that he ruled during the time known as the Long Peace, when Morgoth and his armies were contained by the Siege of Angband. He was succeeded by his son Bregor.
Boromir of Ladros was the first of Men to bear that name, but by no means the last. A short-lived StewardBoromir ruled Gondor during the twenty-fifth century of the Third Age and, rather more famously, Boromir of the Company of the Ring also took his name from this immensely distant ancestor.
Notes
1
These dates are taken from a genealogy of the House of Bëor reproduced in volume XI of The History of Middle-earth (The War of the Jewels). They are not therefore completely canonical, but they do fit the narrative established in The Silmarillion. Boromir was appointed tha first lord of Ladros, and this must presumably have been after his father's death in I 403 (otherwise Boron would have been made lord), but we have no more precise dating for his rule.