LAFAYETTE, La. – In this tradition-rich city known for its crawfish etouffee and Zydeco stomps, high-speed Internet rules. Web videos upload in a few quick seconds. Surgeons review online pathology reports from their living rooms. University students share bulky research files with one another electronically at lightning speeds.

More than 800 miles of fiber-optic cable hum invisibly underground in Lafayette, a city of 120,000, delivering Internet speeds of up to 100 megabytes per second — rare for even major cities. The cutting-edge connectivity in the heart of Cajun country is due not to a private telecom giant but to a public municipal service that offers higher speeds and often lower rates than the private sector...