The county was situated in the Carpathian Mountains, around the sources and upper courses of the rivers Olt and Mureş.
It is named after Ferenc Mikó (1585–1635), who began building it a decade after becoming supreme captain of the Csíkszék (Ciuc), Gyergyószék (Gheorgheni) and Kászonszék (Caşin) Székely seats, later merged into Csík County.
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