Language-based state reorganization took place across India on 1st November 1956.
Consequently, several states (including Kerala, Karnataka, and Andhra Pradesh) celebrate their statehood days on November 1st.
Step 1: Recall the meaning of Kerala Piravi. "Kerala Piravi" literally means "Birth of Kerala" in Malayalam. It commemorates the formation of the state of Kerala. Step 2: Identify the date of formation. Kerala was formed on November 1, 1956, when Malayalam-speaking regions of Travancore-Cochin and parts of the Madras state were merged into one state. Step 3: Confirm the answer. Kerala Piravi Day is celebrated every year on November 1st to mark the state's founding. \[ \boxed{\text{1st November}} \]