Johnson is a privately owned irrigation dam located in Franklin, Idaho, near the city of Preston. Built in 1860, this earth dam stands at a height of 27.6 feet and has a storage capacity of 396 acre-feet. The dam is primarily used for irrigation purposes and is regulated by the Idaho Department of Water Resources.

With a significant hazard potential and a fair condition assessment as of July 2018, Johnson Dam is closely monitored and inspected by state regulatory agencies to ensure its safety and functionality. The dam has a spillway width of 20 feet and features slide gates as outlet controls. Despite being modified over the years, the dam still maintains its original purpose and design, serving as a vital water resource for the surrounding area.

Located along Worm Creek and Cub River, Johnson Dam plays a crucial role in water management and agricultural activities in the region. With a moderate risk assessment and regular inspections, this historic structure continues to contribute to the local economy and environment while highlighting the importance of sustainable water resource management in the face of changing climate conditions.