Table schema:
CREATE TABLE table_name_68 (county VARCHAR, listed VARCHAR, construction_completed VARCHAR)

Question: In what county is the entry that has a Construction Completed date of 07/19/2000 and a Listed date of 09/21/1984 located?
SQL: SELECT county FROM table_name_68 WHERE listed = "09/21/1984" AND construction_completed = "07/19/2000"