Of the 64,124 cases reported to the United States Sentencing Commission in fiscal year 2023, 21,504 involved non-U.S. citizens. Non-U.S. citizens accounted for 33.7% of all individuals sentenced in fiscal year 2023 (USSC Quick Facts available here).
This Government Accountability Office report provides publicly available information on incarcerations of noncitizens in the U.S., not just federal facilities.
Findings include that federal agencies don't collect citizenship information for all people in state and local facilities, where about 90% of incarcerated people are held. The number of noncitizens incarcerated by the Bureau of Prisons at the end of 2022 was 33% less than at the end of 2017. The number of noncitizens sentenced for federal crimes in FY 2023 was 27% less than in FY 2018. Of the noncitizens sentenced for federal crimes in FY 2018-2023, 76% were sentenced for immigration crimes.