The Lower Sioux Agency, or Redwood Agency, was the federal administrative center for the Lower Sioux Indian Reservation in what became Redwood County, Minnesota, United States. It was the site of the Battle of Lower Sioux Agency on August 18, 1862, the first organized battle of the Dakota War of 1862.

The Attack at the Lower Sioux Agency was the first organized attack led by Dakota leader Little Crow in Minnesota on August 18, 1862, and is considered the initial engagement of the Dakota War of 1862. It resulted in 13 settler deaths, with seven more killed while fleeing the agency for Fort Ridgely.