For relevant counties (e.g., USA and Australia), you can target a state within a country by adding to the username-country-country_code-state-state_code. Use only two-letter state codes in lowercase.

curl "http://target.site" \
    --proxy brd.superproxy.io:22225 \
    --proxy-user brd-customer-<CUSTOMER_ID>-zone-<ZONE_NAME>-country-us-state-ny:<ZONE_PASSWORD>