Li’l Sebastian debuted at the Pawnee Harvest Festival in 1987.
The miniature horse was introduced in the season-three episode “Harvest Festival,” when Leslie Knope brings him back as a headline attraction for Pawnee’s revived festival. Leslie explains that his earlier debut at the 1987 festival made him an instant local sensation.
Li’l Sebastian’s reputation is deliberately comic and outsized. Pawnee residents treat him like a major celebrity: the show says he became the eighth most photographed item in the United States during his breakthrough week, and his name reportedly became extraordinarily popular among Pawnee children.
The year is sometimes confused with the episode’s broadcast date. “Harvest Festival” aired in 2011, but the question asks about the fictional history of Li’l Sebastian within Pawnee, not the year the character first appeared on television. His debut is therefore 1987.