(Unless otherwise noted, all data is as of the 1860 census.)

Total number of slaves in the Lower South : 2,312,352 (47% of total population).

Total number of slaves in the Upper South: 1,208758 (29% of total population).

Total number of slaves in the Border States: 432,586 (13% of total population).

Almost one-third of all Southern families owned slaves. In Mississippi and South Carolina it approached one half. The total number of slave owners was 385,000 (including, in Louisiana, some free Negroes). As for the number of slaves owned by each master, 88% held fewer than twenty, and nearly 50% held fewer than five. (A complete table on slave-owning percentages is given at the bottom of this page.)

For comparison's sake, let it be noted that in the 1950's, only 2% of American families owned corporation stocks equal in value to the 1860 value of a single slave. Thus, slave ownership was much more widespread in the South than corporate investment was in 1950's America.

On a typical plantation (more than 20 slaves) the capital value of the slaves was greater than the capital value of the land and implements.

Slavery was profitable, although a large part of the profit was in the increased value of the slaves themselves. With only 30% of the nation's (free) population, the South had 60% of the "wealthiest men." The 1860 per capita wealth in the South was $3,978; in the North it was $2,040.

Selected Bibliography

1. Battle Cry of Freedom, by James McPherson
2. Ordeal by Fire, by James McPherson
3. The Confederate Nation, by Emory Thomas
4. Civil War Day by Day, by E.B. Long
5. Ordeal of the Union (8 vols.) by Allan Nevins
6. Reader's Companion to American History, by Eric Foner and John Garrity

An especially interesting journal paper (might require access to a library that allows Interlibrary Loan) is the following:

Otto Olsen, "Historians and the Extent of Slave Ownership in the Southern United States,"  Civil War History, Vol. 18, No. 2, June 1972, pp. 101--116.

Census data can be appealed to in order to determine the extent of slave ownership in each of the states that allowed it in 1860. The figures given here are the percentage of slave-owning families as a fraction of total free households in the state. The data was taken from a now-inactive census archive site at the University of Virginia, but the National Archives has it online here.  (I hope they don't change that link on me!)

In the Lower South (SC, GA, AL, MS, LA, TX, FL -- those states that seceded first), about 36.7% of the white families owned slaves. In the Middle South (VA, NC, TN, AR -- those states that seceded only after Fort Sumter was fired on) the percentage is around 25.3%, and the total for the two combined regions -- which is what most folks think of as the Confederacy -- is 30.8%. In the Border States (DE, MD, KY, MO -- those slave states that did not secede) the percentage of slave-ownership was 15.9%, and the total throughout the slave states was almost exactly 26%.

An interesting discussion about how many Confederate soldiers might have owned slaves, along with pointers to other sources, can be found here. Another good source is this book.