Los Angeles County lost 184,465 residents between July 2020 and July 2021 -- the largest numeric population decline of any county in the United States that year, per the Census Bureau's own estimate. San Francisco County lost 58,764 -- less than a third as many people, in raw human terms.[1] One of these cities spent the next two years as the country's go-to symbol of pandemic-era urban flight. The other one didn't become a symbol of anything.
The reason the two rankings point in opposite directions is arithmetic, not narrative -- and it's the Census Bureau's own numbers that make the mechanism visible. Manhattan (New York County) posted the steepest percentage decline of any large US county in 2020-2021, -6.9%, on a numeric loss of 117,375 people. San Francisco was second-steepest nationally at -6.7%, losing 58,764.[1][2] Cook County, Illinois -- metro Chicago's core -- lost nearly twice San Francisco's headcount, 102,395 people, but against a population base more than six times larger, that comes out to a 1.9% decline.[1][3] Los Angeles County's 184,465-person loss, the biggest in the country, lands at just 1.8% against its roughly 10 million residents.[1] A small, dense county loses a modest number of people and posts a dramatic-sounding rate. A sprawling county loses more people than anywhere else in America and posts a number that reads as unremarkable. Boston's Suffolk County split the difference -- a roughly 3% decline, large enough to register but never enough to carry its own exodus narrative the way New York's and San Francisco's did.[2]
Both of the leading counties also lost their populations from the same specific place: people in their 20s and early 30s. Manhattan's population aged 20-34 fell 13.6% in that one year; San Francisco's fell 15.5% -- more than double each county's own overall decline rate.[2] That's the demographic the "young professionals fleeing the city" story was actually describing, and the Census data confirms it happened. What the percentage framing obscured is that it happened at a genuinely small scale next to what was moving out of Los Angeles and Chicago at the same time.
Census's county population estimates measure something broader than moving vans -- births, deaths, and international migration are folded in alongside domestic moves. To isolate the actual migration, and to see where people who left actually went, this site pulled IRS Statistics of Income county-to-county migration data directly from the source for the first time -- real address changes between one tax filing year and the next, at the county level, for every year from 2019-2020 through 2022-2023.[4] Measured this way, net domestic out-migration in 2020-2021 ran 232,706 for New York City's five boroughs, 141,542 for Los Angeles County, 83,939 for Cook County, 31,296 for San Francisco County, and 24,568 for Boston's Suffolk County.[4] On pure domestic migration, New York's outflow was the largest of any metro checked here by a wide margin -- more than seven times San Francisco's. Los Angeles was second. San Francisco, the city whose exodus got the most sustained coverage, ranked fourth of the five.
The IRS data also shows exactly where New York's outflow landed, and it wasn't scattered nationwide. Excluding moves between the five boroughs themselves, the largest single destinations in 2020-2021 were Nassau County (33,877 people), Westchester County (23,418), and Suffolk County, NY (19,995) -- New York's own suburban ring -- followed by Hudson, Bergen, Essex, Middlesex, and Monmouth counties in New Jersey and Fairfield County, Connecticut.[4] The people the city lost mostly didn't leave the region. They moved to the counties around it.
Update, August 26, 2026: A finer breakdown of that suburban ring sharpens the picture further. Splitting it by state for the same 2020-2021 year, New York's own suburbs -- just Nassau and Westchester counties -- took in 57,295 people, more than all five of the largest New Jersey destination counties (Hudson, Bergen, Essex, Middlesex, and Monmouth) combined, 47,721.[4] New York kept more of its own outflow inside the state than New Jersey absorbed, a distinction most coverage of the period didn't draw this precisely. Florida held up as a real, separate destination in its own right -- Miami-Dade, Broward, and Palm Beach together pulled in a consistent 6.5-8.7% of New York's total outflow across all four years on file, in line with New York City's own comptroller's office finding that roughly 19,000 Manhattan movers went to Florida against 20,000 who relocated to Brooklyn.[5] A separate "New Yorkers moving to the Midwest" narrative doesn't hold up nearly as well: every county across twelve Midwestern states combined took in less than half of what Florida alone did.[4]
None of the underlying reporting on San Francisco's population loss was inaccurate -- the city really did lose a sixth-highest-in-the-nation share of its 20-somethings, and the Census Bureau's own -6.7% figure is real. What went unreported alongside it is that percentage decline and human scale are different measurements, and only one of them is what a reader pictures when a story says a city is emptying out. A county losing 6.7% of 815,000 people sounds, and was covered as, more dramatic than a county losing 1.8% of 10 million -- even though the second number describes three times as many actual households packing up and leaving. Los Angeles lost the most people of any county in America two years running, and Chicago lost nearly twice San Francisco's headcount, and neither became the story people remember about pandemic-era migration. The story followed the rate. The rate is real. It just isn't the same thing as the size.