Titled "ISIS in America: From Retweets to Raqqa," the report focuses on around 300 people who have been identified as American recruits or supporters of the terrorist organization.
The diverse group ranges in age from 15 to 47 with an average age of 26 years; 40% are converts to Islam; about one in 10 are women; and more than half have traveled or have tried to travel abroad, the report says.
The sympathizers connect with the terror group online – especially via Twitter – and in everyday life. Their motivations vary.
"While some seek to join the self-declared caliphate in ISIS-controlled territory, others plan attacks within the US. It's a growing and disturbing phenomenon," co-author Lorenzo Vidino, who directs the Program on Extremism at George Washington University, said in a statement accompanying the report.
The group is among what the FBI estimates is "hundreds, if not thousands, of individuals" who are sympathetic to Daesh, the report says. The bureau has open investigations into recruits in every state.
While it is not new for Americans to join jihadist groups, Vidino says "the size of the ISIS-related radicalization and mobilization is unprecedented."
While the report says that most of the sympathizers will never "make the leap from talk to action," it also acknowledges that some will turn to real militancy – whether at home or abroad.
"Because there is no standard recruit profile, there is also no silver bullet that will blunt ISIS's allure. Recognizing this complexity is a vital initial step for policymakers, law enforcement officials, civic leaders, teachers and parents when crafting effective solutions."