1630s, from un- (1) "not" + past participle of concern (v.). Related: Unconcernedly.
the average American...is unconcerned that his or her plight is the result of a complex of personal and economic and governmental actions...beyond the normal citizen's comprehension and control
blithely unconcerned about his friend's plight
the prisoner seems entirely unconcerned as to the outcome of the examination
readers unconcerned with style