On the radio, maybe hear America's checking who's in the country (6)
I believe the answer is:
census
'on the radio maybe hear america's checking' is the definition.
I can't tell whether this definition defines the answer.
'in the country' is the wordplay.
'in the' becomes 'cens' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'country' becomes 'US' (United States).
'cens'+'us'='CENSUS'
'who's' acts as a link.
Can you help me to learn more?
(Other definitions for census that I've seen before include "Periodic count as of population" , "Head-count" , "People count" , "Population survey" , "Official body count?" .)