Falls City is located in northwestern Karnes County, about 44 miles (71 km) southeast of the center of San Antonio, on the left (north) bank of the San Antonio River at 28°59′N 98°1′W / 28.983°N 98.017°W / 28.983; -98.017 (28.9807, –98.0196).

[6] It is traversed by the Union Pacific Railroad and US Route 181 (Front Street).

It is 10 miles (16 km) northwest of Karnes City, the county seat.

[4] As of the 2020 United States census, there were 514 people, 338 households, and 257 families residing in the city.

The climate in this area is characterized by hot, humid summers and generally mild to cool winters.