During the intervals between each census of population required under section 141 of this title
, the Secretary, to the extent feasible, shall annually produce and publish for each State,
county, and local unit of general purpose government
which has a population of fifty thousand or more, current data on total population and population characteristics and, to the extent feasible, shall biennially produce and publish for other local units of general purpose government current data on total population. Such data shall be produced and published for each State,
county, and other local unit of general purpose government
for which data is compiled in the most recent census of population taken under section 141 of this title
. Such data may be produced by means of sampling or other methods, which the Secretary determines will produce current, comprehensive, and reliable data.