Every other Spanish word that has a "J" follows a different rule:

 - San Jose 
 - La Jolla 
 - San Juan 
 - Jiminez

Why is San Jacinto not pronounced San Hacinto in English?

The article mgb links to below shows that the J in Jacinto is under attack in Texas, but it doesn't explain why Texans don't pronounce Jacinto like every other Spanish J word. Thanks for the link mgb.