The tally of slaves in New York is given in the 1855 census, county
by county.  This is not a perfect number but is probably a close count.
And of course, not all African Americans were freed in 1827; those under
age were continued until they reached maturity.

>Today in 1827 brought final emancipation to New York State.
>I am trying to find out how many remaining slaves there were in New York
>State who were emancipated on 4 July 1827.
>I should be grateful for any help towards finding the number, and if
>possible the demographic distribution. Names of newspapers current at
>that date would be useful in the absence of hard data, though collections
>here in the UK might be patchy.
>John Weiss <[log in to unmask]>
>Researching the four thousand Black Americans
>who took their freedom in the War of 1812