Waterjet systems including control valves and associated devices, systems, and methods are disclosed. A waterjet system configured in accordance with a particular embodiment includes a fluid source, a jet outlet, and a fluid conveyance extending from the fluid source to the jet outlet. The system further includes a control valve positioned along the fluid conveyance downstream from the fluid source and upstream from the jet outlet. The fluid conveyance has a first portion upstream from the control valve and a second portion downstream from the control valve. The control valve is configured to controllably reduce a pressure of fluid within the second portion of the fluid conveyance relative to a pressure of fluid within the first portion of the fluid conveyance. The first portion of the fluid conveyance is configured to accommodate movement of the jet outlet relative to the fluid source.