1690s, "conversion to secular purposes," originally in reference to Church property; see secularize + noun ending -ation. General meaning "state of having become secular" is by 1863.
Entries linking to secularization
secularize v.
1610s, of property, offices, etc., "make secular, convert from ecclesiastical to civil use," from secular + -ize. From 1711 as "to become worldly;" from 1846 in reference to education, social institutions, etc., "divest of religious observances or influences." Related: Secularized; secularizing.