Final answer:
South Carolina was the first state to secede on December 20th, 1860.
Step-by-step explanation:
The first state to secede on December 20th, 1860 was South Carolina. They called a convention and voted unanimously (169-0) to dissolve their union with the United States. Other states in the deep South quickly followed suit, including Mississippi, Florida, Alabama, Georgia, Louisiana, and Texas.