I am assuming you mean "seceded to FORM the Confederate States of America," as states did not secede from the Confederacy....
The Confederacy claimed 13 states: South Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, and Texas were the first seven, and then once the war began, North Carolina, Tennessee, Arkansas and Virginia also seceded. Kentucky and Missouri *never seceded* but the Confederacy claimed them anyway.
And the Union never recognized the Confederacy as a legal entity -- but that is another discussion!