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.

Tensions had run high in the weeks leading up to the attack. Many eastern Dakota were angered by the refusal of traders to extend credit during a summer of starvation and hardship, and the failure of the United States Indian agents to deliver annuity payments as required by treaty. The initial attack on the Lower Sioux Agency by a faction of the eastern Dakota focused on the four trading stores, which they proceeded to raid for flour, pork, clothing, whiskey, guns, and ammunition.

The attack at the Lower Agency was followed by the Battle of Redwood Ferry. Violence soon spread to isolated farms and settlements in Brown and Renville Counties, with an estimated 200 settlers killed and another 200 captured. Some settlers’ lives were saved after they were warned by the Dakota to flee.

After the initial conflict at Acton Township, Minnesota on August 17, in which five white settlers were killed by four young Wahpeton Dakota hunters from Rice Creek village, tensions were running high. Similar incidents in the past had resulted in only the perpetrators being punished. However, "traditionalist" leaders such as Cut Nose, the "head soldier" of the soldiers' lodge, and Red Middle Voice, the head of the Rice Creek band, grasped that the situation presented an opportunity to lead an uprising against the Americans, who had withheld annuity payments and provisions during a summer of starvation and hardship for many eastern Dakota. They were also aware that the Americans were in the midst of their own Civil War, and were "getting short of men".

In the middle of the night, Red Middle Voice and his nephew, Chief Shakopee III (also known as Little Six), convened a council at Little Crow's house. Taoyateduta Little Crow was viewed as "the last of the major Mdewakanton chiefs to hold out against acculturation", whose support was essential to convincing others to go to war. Although Little Crow initially hesitated, warning that it was futile to go to war against the Americans, he eventually agreed to lead an uprising, and ordered an attack on the nearby Lower Sioux Agency the following morning.

On the morning of August 18, several traders happened to be away from the Lower Sioux Agency, including Nathan Myrick, Major William H. Forbes, and Captain Louis Robert, leaving others in charge of their stores.

In the early morning, a group of Dakota soldiers marched toward the Lower Sioux Agency, also known as the Redwood Agency. Dominant within the group were men from the villages of Red Middle Voice and Shakopee. They were joined by others from the villages of Mankato, Big Eagle, and Little Crow. Chief Wabasha III opposed the war and refused to lead a group. Several Dakota men and women went to warn their relatives and friends living in the vicinity.

Many leaders lacked control over their bands, as young braves acted without heeding their warnings. Historian Gary Clayton Anderson argues that the soldiers' lodge or akicita from Shakopee's village asserted authority in leading the attack, given Shakopee's inexperience as a leader, and the age of his elderly uncle, Red Middle Voice. Anderson also suggests that the pattern of killing seemed "selective", with those perceived as having insulted Dakota religion or medicine men, or who had refused to assist the Dakota with food or credit, targeted first. One young soldier, Tawasuota (Much Hail), was one of the first to attack.