Flatirons Bank Share: Banks Flatirons Bank Visit Website Request Info 522 4th Avenue Longmont, CO 80501 303-530-4999 303-530-4735 (fax) https://flatirons.bank/ About Map About Flatirons Bank is a locally-owned, independent financial institution dedicated to serving Boulder County. What's Nearby? Distance: 5 10 15 20 25 50 mi.