The announcement came as the Ugandan army suspended a search for Kony in the Central African Republic (CAR), blaming “hostility” from its new government.
Kony, leader of the Lord’s Resistance Army, is wanted by the International Criminal Court for alleged war crimes.
He and his fighters are thought to be in the CAR or neighbouring countries.
US authorities say the reward is also being offered for information on two other top LRA leaders, Okot Odhiambo, and Dominic Ongwen.
The LRA has “tormented and terrorized children” in Uganda and across the region, US Secretary of State John Kerry wrote in the Huffington Post on Wednesday.
Mr Kerry said Kony and other LRA leaders “will not be easy to find”, adding: “The LRA is broken down into small bands of rebels, scattered throughout dense jungle, hidden by dense canopy, controlling territory through tactics of fear and intimidation.”
Decades of war
Earlier, Ugandan troops in the CAR suspended their hunt for Kony and returned to their bases in the country.
Rebel forces took power 10 days ago in the CAR and ousted President Francois Bozize, whose government was a supporter of the mission to find Kony.
The Ugandan forces are in the CAR under an African Union mandate, assisted by soldiers from other African nations, as well as US special forces.
The African Union suspended the CAR’s membership after the Seleka rebel group seized power and overran the capital, Bangui.
“We have reorganised our forces, collected them in defence, as we await the decision that will follow consultations going on between the African Union and participating countries,” Ugandan army spokesman Col Felix Kulaijye told the BBC.
Joseph Kony and the estimated 200-500 fighters of his Lord’s Resistance Army (LRA) have waged war in Uganda and the region for more than two decades.
He claims the LRA is fighting to install a government in Uganda based on the Biblical Ten Commandments.
But his rebels now terrorise large swathes of the Democratic Republic of Congo, South Sudan and the CAR and he is wanted by the International Criminal Court for rape, mutilation and murder of civilians, as well as forcibly recruiting children to serve as soldiers and sex slaves.