Jamey,
If it is of interest to you or others:
The term "established Church" was more often used in the 1600's by separatists and dissenters, and only came to be more popularly used in the 1700's and 1800's, as the "established Church" in Britain became less and less the national Church with the rise of tolerated denominations.
The older preferred language was
circa sacra (the magistrate's authority around
sacred things) and a national Church.
Circa sacra is a more accurate and comprehensive term for the Biblical and reformed view of such matters.
If it is of interest, I give an introduction to
Circa Sacra from the older, 1600's reformed writers in this paper:
On the difference between the Reformation's
circa sacra and the later 1800's Establishment Principle, especially as espoused by the Free Church of Scotland, the establishment principle being a reduction of
circa sacra, see p. 6, footnote 9, but especially the section on the topic, pp. 84-104.