Page 28, Appendix II, Countering Violent Extremism: Actions Needed to Define Strategy and Assess Progress of Federal Efforts, United States Government Accountability Office
...between September 12, 2001 and December 31, 2016. During this period, no persons in the United States were killed in attacks carried out by persons believed to be motivated by extremist environmental beliefs, extremist "animal liberation" beliefs, or extremist far left beliefs.
What is the Threat to the United States Today?, New America
Since 9/11, jihadists have killed 107 people inside the United States. This death toll is similar to that from far-right terrorism (consisting of anti-government, militia, white supremacist, and anti-abortion violence), which has killed 122 people.
Page 18, Homeland Threat Assessment, U.S. Department of Homeland Security:
Among DVEs (Domestic Violent Extremists), racially and ethnically motivated violent extremists — specifically white supremacist extremists (WSEs) — will remain the most persistent and lethal threat in the Homeland.