One scary sentence from the linked blog post:
"Since the 1990s, the map shows isolated, lightly populated counties with heavily male populations: those are the counties with prisons."
Prisoners live in a geographical location.
Seems kind of obvious that prisoners living within the bounds of a geographic area would be included in counts of people living in that geographic area.
I think, viewed more carefully, one would be forced to recognize that the effect described results instead from the policy of allocating money for programs by total Census counts without considering the fitness of those counts to the purpose of the particular programs and making suitable adjustments (and that that policy is going to have some infelicities, if not the exact same ones, no matter what general policies are adopted for Census counts.)