The number of banking institutions in the U.S. has dwindled to its lowest level since at least the Great Depression, as a sluggish economy, stubbornly low interest rates and heightened regulation take their toll on the sector.

The number of federally insured institutions nationwide shrank to 6,891 in the third quarter after this summer falling below 7,000 for the first time since federal regulators began keeping track in 1934, according to the Federal Deposit Insurance Corp.

...