Little Hawk wanted to see comparative figures on the US population for the same period. I will cede that these numbers will show a decrease in the % of slaves to the general poulation from 18% in 1820 (peak) to 17% in 1840 to 14% in 1860. Yhis would seem to suggest a net decline in slave population especially in the 20 year immediately preceding the Civil War. But as bobert says, numbers can be misleading. That 20 year period saw the first massive immigration movement from Europe (the Irish Potato Famine) and the vast majority of these immigrants settled in the industrialized cities in the North.
In the slaveholding states you do not see a net decrease in slave population.In South Carolina , for example, there was a net increase from 56% in 1840 to 59% in 1860, due largely to the labor intense rice growing industry. Is it any wonder that SC was the most vocal of all the pro-slavery forces and the first state to secede from the Union.
    Back in 1787 slavery was such a hot-buuton issue that the only way to get the US Constitution ironed out and ratified by all states was by way of a tacit agreement on all sides to not even discuss it. The word "slave" is not to be found in the entire document. The unspoken gist of this "gentlemens'" agreement was that northerners wouldn't push for the ending of slavery by legislations and the southerners would gradually phase it out. Fifty years later, the real number of slaves and the net % of slaves in the US population were at an all time high. It is at this point that the Abolitionist movement began. (There had been voices, mostly Quaker, speeking against slavery clear back to the early 1700's, but no large scale national
Abolition movement until the 1830's.)
   Bobert says that "these people were no better off from the Emancipation right up until the 20's when their grandkids had some opportunities...". This isn't entirely true. Emancipation did come at the beginning of the opening of the West (the plight of its original inhabitants could be subject of another thread). At least 1/3 of all cowboys were black (another 1/3 was Mexican. Funny how you never see this in the movies.), living and working under the same conditions as their white counterparts. Not the most comfortable life, but surely, better than that of a 7 year old white kid working 72 hours a week in some New England textile mill or an Irshman doing deep pit mining in Pennsylvania. But, nevertheless, I will concede that sharecropping and Jim Crow were no great improvement over slavery, however emancipation was only the first step in the equal integration of black people into American society which is still an ongoing struggle. Every process begins with a first step. How many opportunities would have opened up for the grandchildren of 1860's slaves if those grandchildren were themselves, still slaves.