Philadelphia remains the sixth-largest city in the United States, but its hold on that ranking is becoming increasingly precarious as a fast-rising Texas city is now knocking at the door, writes Dana Munro for The Philadelphia Inquirer.

New U.S. Census Bureau estimates put Philadelphia’s population at roughly 1.57 million residents as of mid-2025. 

San Antonio, once a distant rival, has surged to about 1.55 million. The gap between the two cities was 160,000 people in 2020. However, the number has now collapsed to just 26,000. 

At the current pace, Philadelphia’s long-held rank as the sixth-largest city in the United States could be gone within years.

One key reason for San Antonio’s rapid rise is annexation. Through this process, cities expand their geographic boundaries to absorb surrounding land and population growth. 

Philadelphia, by contrast, has been effectively frozen in place since the 1854 Consolidation Act, when the city and county merged into a single jurisdiction. 

However, that’s not to say that Philadelphia doesn’t have a silver lining. 

Experts point to the city’s dense housing stock, robust public transit network, diversified economy, and steady immigration-driven population gains as signs of underlying resilience.

While other cities are growing, Philadelphia is standing still.

The question now isn’t just whether Philadelphia will be overtaken by San Antonio, but rather what the city is willing to do about the structural forces that made the gap closeable in the first place?

For the full report on how demographic shifts and annexation policies are reshaping America’s largest cities, read The Philadelphia Inquirer.

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