The four border states that did not secede and therefore remained loyal to the Union during the Civil War were Delaware, Kentucky, Maryland and Missouri. In addition, 50 Virginian counties chose to remain loyal to the Union despite Virginia's secession, and these counties eventually became the state of West Virginia.
Between the election and inauguration of President Lincoln, seven states seceded from the rest of the country. After the attack on Fort Sumter, four more states seceded. President Lincoln was determined to keep the aforementioned border states from leaving too, and he tried to sway them by making the war about the preservation of the nation rather than the abolishing of slavery. Although these states did not secede, some volunteers from these states did work to aid the cause of the Confederacy.