It sounds like the city was founded in honour of Saint Francisco (San francisco de Asis).
In order to differenciate it from other places, comes after the "real" place name:
San Francisco de Cuellar. If you make the same in Texas, it would be San Francisco de Texas, where "de" means not the Saint's born place (Asis) but the location.
Saludos
PD: for example
here you can see different Saints but the second name indicates a places and not the Saint's born place (San José del Parral,San Pablo de Balleza, Real de Santa Eulalia de Mérida de Chiguagua]
PD I found it in the same link
Quote:
|
El 12 de octubre de 1709, se expidió el decreto que autorizó la fundación del Real de San Francisco de Cuellar, actual ciudad de Chihuahua, en honor del Virrey de la Nueva España, Marqués de Cuellar y de la orden de San Francisco de Asís.
|
It's a double name, in honour of "San francisco" (for de order) + "de Cuellar" (for the vice-king at the time, Marquis of Cuellar")