Frontier province of the Viceroyalty of New Spain in what is now northeastern Mexico, granted to Luis de Carvajal y de la Cueva by Philip II in 1582 and named for the Kingdom of León in Spain.
Remained functionally autonomous on the northern frontier; folded into the Eastern Internal Provinces (Provincias Internas de Oriente) in 1786, then ended with Mexican independence in 1821.
The atlas holds 2 border frames for New Kingdom of León (Nuevo Reino de León) — the shape you scrub through changes in 1582 · 1600.
The standard scholarly history of exactly this province, from its Carvajal-era founding through the early 18th century (Spanish-language; no comparable English-language monograph found on Open Library).