The New Jersey Office of Homeland Security and Preparedness (NJOHSP) has released their annual report. NJ is unusual in their efforts to make such info readily available to the general public.
It looks like NJ is following the FBI model of differentiating between Homegrown Violent Extremists (Americans who do violent stuff in America in support of foreign terrorist groups like ISIS) and foreign terrorists like ISIS who travel to the US to kill Americans.
The first group is high risk, the latter, low.
To clarify, the reason it's important to differentiate between homegrown and foreign terror is the choice of victims.
Foreign groups like ISIS want to kill Americans and attack American institutions. Homegrown extremists who support ISIS are more likely to attack synagogues, Jewish schools, and other places where Jews congregate.
I also expect that narcoterrorism and gang-related terrorism are going to make their way on this list in the foreseeable future.
Three High-Ranking MS-13 Leaders Arrested on Terrorism and Racketeering Charges
https://www.justice.gov/opa/pr/three-high-ranking-ms-13-leaders-arrested-terrorism-and-racketeering-charges