I found this 3 page document which mentions "La Provincia de Texas of Nueva Espana (Mexico)." Year 1692.

That is the earliest I have seen the existence of Texas as a Province of Nueva Espana (Mexico) being mentioned. Supposeldy, Texas would be under the political jurisdiccion of "Real Audencia Government of Guadalajara, Jalisco (Nuevo Galicia), Mexico (Nueva Espana) and also under the Catholic Religious Order of the Bishop of Guadalajara, Jalisco Mexico.

http://www.archivesportaleurope.net/web/guest

Reference No. MEXICO,66,R.2,N.2