The slender-billed grackle was a species of grackle in the Icteridae family of birds. The species was closely related to the western clade of the great-tailed grackle, from which it diverged quite recently, around 2,000 years ago. The slender-billed grackle was endemic to central Mexico, especially in the Valley of Mexico and the Toluca Valley. Early observations recorded by Franciscan friar Bernardino de Sahagún in the 16th-century manuscript General History of the Things of New Spain indicate that the species was found in cultivated areas and towns. Later records indicated that it might be a marsh specialist. The species became extinct around the turn of the 20th century.