New York's 21st State Assembly district is one of the 150 districts in the New York State Assembly.

It has been represented by Judy Griffin since 2025, defeating Brian Curran.

Historically, President Theodore Roosevelt began his political career representing the 21st district from 1882 to 1884, albeit under entirely different lines.

The district was previously based in Manhattan; in Roosevelt's time it included the "Silk Stocking District" of the Upper East Side.

It includes the town of Hempstead, and contains the villages of Lynbrook, Rockville Centre, Malverne, South Hempstead, Baldwin and parts of Freeport, West Hempstead, Oceanside, East Rockaway, Lakeview, Hewlett, Hempstead, Franklin Square, and Valley Stream.