county (n.)

mid-14c., “a shire, a definite division of a country or state for political and administrative purposes,” from Anglo-French counte, from Late Latin comitatus “jurisdiction of a count,” from Latin comes (see count (n.1)). It replaced Old English scir “shire.”

From late 14c. as “the domain of a count or earl.” County palatine, one distinguished by special privileges (Lancaster, Chester, Durham) is from mid-15c. County seat “seat of the government of a county” is by 1848, American English.

shire (n.)

Old English scir “administrative office, jurisdiction, stewardship, authority,” also in particular use “district, province, country,” from Proto-Germanic *skizo (source also of Old High German scira “care, official charge”). Ousted since 14c. by Anglo-French county. The gentrified sense is from The Shires (1796), used by people in other parts of England of those counties that end in -shire; sense transferred to “hunting country of the Midlands” (1860).