In 1860 (or any other year) BEFORE The U.S. Civil War, Were There More Free African Americans In The North Or The South?

In today's LunchBunch Chat Session at AfriGeneas, the discussion of the number of FPOC (Free People Of Color) in the north vs. the south was a topic of discussion.

Is there any reliable data that leans towards proving that either the Southern States or the Northern States can claim to have had more free African Americans during that time?

Should the U.S. Federal Census be the only criteria used to make this determination? If not, then how should this be determined?

Has there been any reasonable and/or reliable research to prove either/or?

Please keep in mind, that sources should be cited. Also, what reliable/reasonable criteria is being used to determine the 'race' or ethnicity of the people counted?

Should only people identified (on the Federal census) as "Negro", "Black", "Colored", or "Mulatto" be considered in this study? Are the people who were charged with gathering the info on census', mostly reliable (by today's standards)?

Consider too, that the records are (mostly) all we have to go by. Tell us about research that you know of, or have done.