Here are a few possible sources of the poem. Take your pick:

(1) After the horrific wrecking of the schooner Hesperus on the reef of Norman's Woe, off Gloucester, Massachusetts in 1839, Longfellow was inspired to write one of his best-known poems. One of the bodies washed ashore was, in fact, lashed to a spar. This gave the poet his theme.

(2) The real Hesperus was docked when it was hit by such strong winds that it sailed across the street into the third story of a building. Longfellow had read about the 20 odd shipwrecks from this storm but couldn't get the picture of a woman tied to a mast washed up on shore out of his head. This prompted him to write the poem although he changed the victim from a 45 year old woman to a young girl.

(3) The actual Hesperus was a 3-mast coastal schooner docked at Boston's Long Wharf at the time of the hurricane. The wreck from which the morbid details were obtained was actually the brig Favorite, wrecked on the Norman's Woe rocks just outside of Gloucester Harbor, Massachusetts. The Favorite was indeed a total loss with all on board, including a female.

(4) Apparently, there was a ship named "Herperus." But that's not the one that Longfellow immortalized. His poem is "The Wreck of the Hesperus" (note the "s" in the middle, not the "r").

(5) The Great Blizzards of 1839 inspired the great American poet Henry Wadsworth Longfellow to write The Wreck of the Hesperus

(6) On December 17, 1839 a disastrous storm hit the Atlantic coast, from Boston to Gloucester harbor. Seventeen schooners were wrecked and 40 lives were lost. Unable to sleep after reading the news in the Boston Post, Longfellow sat up one night long after midnight and composed the poem effortlessly.

(7) Henry Wadsworth Longfellow, based his ballad, "The Wreck of the Hesperus," on the destruction of the Helen Eliza, which crashed off Peaks Island's shore in 1869.