Mayor Gavin Newsom says the city will formally appeal the Census Bureau's 2007 estimate as early as Tuesday.
The estimate puts San Francisco's population at just over 764,000 residents. But according to the study by a nonprofit organization that uses economic data to estimate population, the city's residents number about 864,000.
Newsom says the discrepancy means the city is not getting its due share of federal funding for social services.
The study says the undercounting occurred mainly in low-income neighborhoods and areas that have seen an influx of residents following new housing construction.