Name used by Polish dukes from ruling dynasty. It might not be used by someone outside of ruling dynasty in Middle Ages. Mieszko is most probably a diminutive form of [Miecisław], which (the latter) later was wrongly decoded as [Mieczysław], and this form become popular.
Actually, there were four mediaeval Polish rulers called Mieszko, the latter two (high dukes Mieszko III and Mieszko IV) were also rulers of smaller principalities since Poland was otherwise politically fragmented.
― Anonymous User 11/19/2011
2
Call me crazy, but this name reminds me of Mexico.
Mieszko is most probably a diminutive form of [Miecisław], which (the latter) later was wrongly decoded as [Mieczysław], and this form become popular.