Great Western Bank (First Interstate Bank) Share: Banks Great Western Bank (First Interstate Bank) Visit Website 2100 N. Main St. Longmont, CO 80501 303-772-0777 303-729-2727 (fax) www.greatwesternbank.com About Map About Personal and business deposit and loan products, safe deposit boxes, drive-up ATM. What's Nearby? Distance: 5 10 15 20 25 50 mi.