CREATE TABLE table_name_90 (_number___county VARCHAR, year_joined VARCHAR, location VARCHAR)

which # / county is correct for year less than 1981 and chalmers as location?
SELECT _number___county FROM table_name_90 WHERE year_joined < 1981 AND location = "chalmers"
SELECT "_number___county" FROM "table_name_90" WHERE "chalmers" = "location" AND "year_joined" < 1981