The number, from this site's own 2023 ACS ingest, not a secondary report. Of 3,220 US counties in the dataset, Loudoun County, VA has the highest median household income on file: $178,707. The five lowest are all Puerto Rico municipios, bottoming out at Las Marías: $16,170.[1][2][3] That's an 11x gap -- wider than the 4.4x this site already documented between Newark and Palo Alto, and it comes from first-party data this site pulled directly, not a citation of someone else's reporting.
It isn't just income -- three axes, same direction
Population: Loudoun has 427,082 residents; Las Marías has 8,790 -- a 49x difference in scale, on top of the income gap, not separate from it.
[1][2][3] Educational attainment: 64.0% of Loudoun's population 25 and older holds a bachelor's degree or higher; in Las Marías, 16.6% does -- a real, measurable 3.9x gap, from the same Census dataset that produced the income figures above.
[1][2][3]
11x
median household income, Loudoun vs. Las Marías
49x
population, Loudoun vs. Las Marías
3.9x
bachelor's-or-higher share, Loudoun vs. Las Marías
A fourth gap, found trying to complete the picture: Puerto Rico is invisible to the federal crime data
Every other comparison on this site pairs economic data with FBI Crime Data Explorer offense counts, county by county. Puerto Rico can't be included that way -- not because of an ingest limitation on this site's part, but because the FBI's own agency directory carries exactly one entry for the entire territory: a single record, agency name "Puerto Rico," county field literally reading "NOT SPECIFIED," marked as not participating in NIBRS.
[4] The rest of the country is measured at county grain. Puerto Rico is measured, by the same federal system, as one undifferentiated unit -- itself a fifth axis of the same gap this piece is about, not a footnote to it.
What the gap is, and isn't. None of this says anything about the people living in either place -- not their effort, not their choices, not their worth. It says something about where each place sits relative to the country's own federal systems: which one gets counted at fine grain and which one gets counted as a remainder, which one has an income high enough that a single county can out-earn a Puerto Rican municipio elevenfold, and still both places are, on paper, the same country. The number that would resolve this -- "is America unequal" -- is exactly the kind of claim this site has already argued is unanswerable at national scale. Loudoun County and Las Marías, named specifically, with real numbers attached to each, is the version of the question that can actually be checked.