Keep Our Communities Safe Act of 2019 This bill revises provisions related to the authority of the Department of Homeland Security (DHS) to detain aliens. DHS may detain an alien pending a removal decision for any length of time until the alien is subject to a final removal order. DHS must detain certain aliens, such as those convicted of an aggravated felony, beyond certain time limits for detaining an alien. The authority of the Department of Justice to review DHS custody decisions concerning an alien awaiting a removal decision shall be limited to whether the alien may be detained, released on bond, or released with no bond. DHS may release such an alien on bond only if the alien is not a flight risk or risk to the community. For an alien subject to a removal order, DHS may extend the 90-day removal period (generally the window in which DHS has to remove an alien after a final order of removal) in certain instances, such as when the alien's removal is stayed during an appeal. DHS may continue to detain an alien beyond the removal period and any removal period extensions. DHS shall periodically certify a justification for detaining an alien beyond the removal period. DHS shall establish a detention review process for aliens who (1) have made all reasonable efforts to comply with a removal order, and (2) are not subject to mandatory detention. DHS shall use the review process to determine whether an alien should be detained or released with conditions.