Lowell's Little Acre

Across from a small, grassy park dedicated to Greek and Irish immigrants, Joe Cogliano, whose grandparents were Italian, sells mangoes to Hispanic customers from the back of his truck. Children play tag while chattering in Spanish on O'Brien Terrace, part of a housing project built in 1939 for Irish laborers. The pungent odor of Vietnamese fish sauce fills a Southeast Asian restaurant where Giavis' Greek grocery once thrived for more than 70 years.

In Lowell they call it the Acre. Less than one-seventh of the current 105,000 citizens of this Massachusetts mill town call it home. But tens of thousands of...