Population census: China conducts population census every 10 years. The first time was in 1953, the second time 1964; the third time 1982; the forth time 1990; the fifth time 2000; the sixth time 2010, the seventh time 2020. The database China Geo-explorer II provides county level data on the 2000 and 2010 census. Earlier census data at country level can be found at the database China Data Online. County level census data from 1982 and 1990 can be found in print in most provinces.
Social & economic census: the database China Data Online (CDO) has some of the data.