Maryland, Missouri, Kentucky, Delaware, and West Virginia.
But it only takes one to disprove the claim that they were fighting for the freedom of black people.
I have to amend my original statement. I said “Slavery had either been outlawed or a path to emancipation was in effect in EVERY northern state at the outbreak of the war” but further research shows that to be inaccurate. Almost every state had a path to emancipation. Every state struggled with the proposition - to varying degrees of success. Every northern state had drawn down its slave populations, typically by manumission or “Selling them south”. Resistance to emancipation remained high in the border states and slavery advocates remained numerous and influential. Each of the border states showed an inclination toward abolition, but at a much slower rate than I was led to believe. Here is what I found state by state:
Maryland:
Maryland held a constitutional convention. A new state constitution was passed on November 1, 1864, and Article 24 prohibited the practice of slavery.
Missouri:
On January 11, 1865, the delegates of the state convention led by Charles Drake passed the immediate emancipation of all enslaved persons in Missouri.
Kentucky:
Controversial laws in 1815 and 1833 limited the importation of slaves into Kentucky, which created the strictest rules of any slave state. The Nonimportation Act of 1833 banned any importation of slaves for commercial or personal purpose. The ban was widely violated, especially in counties near the Tennessee border. Slavery was the principal issue that led to the third constitutional convention held in 1849 where the prohibition was repealed.
Delaware:
Delaware was a test case for Lincoln’s proposed compensated emancipation. President Lincoln focused on Delaware as a possible model for his compensated emancipation plans because there were less than 1800 slaves held in the state – fewer than 2% of its population. If it proved viable it would serve as an example of negotiated abolition. It failed - and cost Congressman George P. Fisher his seat in congress.
West Virginia:
Waitman T. Willey, a Senator of Virginia under the aegis of the Restored Government in Wheeling, composed an emancipation amendment to the constitution to be ratified by public vote on March 26, 1863. It became known as the Willey Amendment. It proved symbolic because the enactment of the 13th Amendment superseded it.