CREATE TABLE table_55864 ("CERCLIS ID" TEXT, "Name" TEXT, "County" TEXT, "Proposed" TEXT, "Listed" TEXT, "Construction completed" TEXT, "Partially deleted" TEXT, "Deleted" TEXT)

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?
SELECT "County" FROM table_55864 WHERE "Listed" = '09/21/1984' AND "Construction completed" = '07/19/2000'
SELECT "County" FROM "table_55864" WHERE "Construction completed" = '07/19/2000' AND "Listed" = '09/21/1984'