Lead Inspector General Report to the United States Congress: Operation Inherent Resolve, Quarterly Report and Biannual Report to the United States Congress, April 1, 2019 - June 30, 2019 [open pdf - 6MB]
From the Executive Summary: "Despite losing its territorial 'caliphate,' the Islamic State in Iraq and Syria (ISIS) solidified its insurgent capabilities in Iraq and was resurging in Syria this quarter. [...] CJTF-OIR [Combined Joint Task Force-Operation Inherent Resolve] said that in Iraq the ISF [Iraqi Security Forces] often lacks the ability to maintain hold forces in cleared territory. [...] USCENTCOM [U.S. Central Command] reported that ISIS militants in both countries employed similar tactics of targeted assassinations, ambushes, suicide bombings, and the burning of crops, but this quarter did not carry out large-scale conventional attacks or attempt to take and hold territory for more than brief periods. [...] CJTF-OIR reported based on open source data that ISIS likely retains between 14,000 and 18,000 'members' in Iraq and Syria, including up to 3,000 foreigners. [...] CJTF-OIR reported to the DoD OIG [Department of Defense Office of the Inspector General] that ISIS in Iraq is attempting to expand its influence over populations in the Sunni-majority provinces north and west of Baghdad, and has reorganized its leadership and established safe havens in rural Sunni-majority areas."
U.S. Department of Defense Office of Inspector General: http://www.dodig.mil/