NY 19A begins at an intersection with NY 19 in the hamlet of Fillmore, a former village in the town of Hume. It initially heads north through the northern portion of the community. Outside of Fillmore, the route curves to the northeast and heads through open, cultivated fields as it parallels the Genesee River, located to the southeast of NY 19A. Near the Allegany–Wyoming county line, NY 19A turns to follow a more northerly routing, matching a similar turn in the course of the nearby river.