The nursery rhyme was first published by the Boston publishing firm Marsh, Capen & Lyon, as a poem by Sarah Josepha Hale on May 24, 1830, and was possibly inspired by an actual incident.[1] As described in one of Hale's biographies:

"Sarah began teaching young boys and girls in a small school not far from her home [in Newport, New Hampshire] ... It was at this small school that the incident involving 'Mary's Lamb' is reputed to have taken place. Sarah was surprised one morning to see one of her students, a girl named Mary, enter the classroom followed by her pet lamb. The visitor was far too distracting to be permitted to remain in the building and so Sarah 'turned him out.' The lamb stayed nearby till school was dismissed and then ran up to Mary looking for attention and protection. The other youngsters wanted to know why the lamb loved Mary so much and their teacher explained it was because Mary loved her pet. Then Sarah used the incident to get a moral across to the class:

Why does the lamb love Mary so? Mary so, Mary so?

Why does the lamb love Mary so? The eager children smiled,

Mary loves the lamb, you know, Lamb, you know, lamb, you know,

Mary loves the lamb, you know The teacher’s happy smile.

Authorship controversy
The Redstone School (1798), now in Sudbury, Massachusetts, is the schoolhouse Mary Tyler attended.