As of 2011, how many US volcanoes were considered by most volcano experts to be active?

Of the 280 volcanoes in the 50 US states and its territories, 169, are considered active, according to the latest count published by the United States Geological Survey through the USGS Volcano Hazards Program. Although some US volcanoes are constantly monitored, the last time the USGS offered a count was in 2011.

Volcanoes are classified as “erupting”, “active”, “dormant”, and “extinct”. An extinct volcano has not erupted for 10,000 years and is not expected to erupt again…probably. An active volcano is any volcano that has erupted at least once since during that 10-millennia span; that is, it has erupted at least once since around 8,000 BC. A dormant volcano is an active volcano that is not currently erupting. An erupting volcano is an active volcano that is currently spewing lava, gas, ash, or some combination of these elements.