Tlahualilo is one of the 39 municipalities of Durango, in north-western Mexico. The municipal seat lies at Tlahualilo de Zaragoza. The municipality covers an area of 3,709.8 km².
As of 2010, the municipality had a total population of 22,244, up from 19,882 as of 2005.
The municipality had 159 localities, the largest of which (with 2010 populations in parentheses) were: Tlahualilo de Zaragoza (9,517), El Lucero (Arcinas) (2,622), classified as urban, and San Francisco de Horizonte (Horizonte) (1,657), Jauja (1,101), Banco Nacional (1,072), and San Julio (1,046), classified as rural.