1540s, "held in repute," past-participle adjective from repute (v.). Meaning "supposed to be" is from 1570s. "[N]ot often found in good sources" [OED]. Related: Reputedly.
Entries linking to reputed
repute v.
late 14c., reputen, "believe (that something is so); c. 1400, "to attribute;" early 15c., "deem, consider, regard," from Old French reputer (late 13c.) and directly from Latin reputare "to count over, reckon; think over," from re-, here perhaps "repeatedly" (see re-), + putare "to judge, suppose, believe, suspect," originally "to clean, trim, prune" (from PIE root *pau- (2) "to cut, strike, stamp"). Related: Reputed; reputing.