The race fannini is found along the Pacific coast of North America from southeastern Alaska to coastal Washington. Its range limits south of Florida are uncertain but many believe that they inhabit many Caribbean islands as well. It has occurred in Yucatan, Mexico, but has not been confirmed to be breeding there. Population sizes have been difficult to determine, because nesting sites are often highly dispersed. The Florida Bay population of occidentalis has been estimated to include 2,500 adults.
Southern populations appear to be more sedentary.
The winter range is in Florida, Cuba, Jamaica, the Antilles and South America, whereas mid western individuals follow the Mississippi River drainage to winter in Cuba and Central America. Great Blue Herons disperse widely after nesting. Herons have no natural predators but great damage is done however to their eggs and nestlings by the crow, ravens, bald eagles, gulls, and raccoons. Bald Eagles are especially a problem given the desire to return their population status. Great Blue Herons have been known to simply leave the nest and young if bald Eagles are roaming the territory.