According to various sources, including foreignpolicy.com, the CIA has confirmed a total of seven countries the US has overthrown, beginning with Iran in 1953. It was the involvement of the military government installation in Syria that tied the US to the ousting of Iran's then Prime Minister Mohammed Mossadegh. Much of this information about the US involvement in the regime change can now be seen in the unclassified documents regarding this coup.
It wasn't until Guatemalan President Jacobo Árbenz turned on the US that anything was done about the then leader and ally of America. After attempting to occupy and essentially take US holdings and property, the US government orchestrated a coup in 1954, resulting in the expulsion of Árbenz.
The US actions in dealing with the former and first Prime Minister of the Congo, Patrice Lumumba, were actions of necessity. Lumumba was removed from office during a conflict with Belgium, a country that the US supported. After leaving office, however, Lumumba began working with the Soviet Union and quickly become a threat to the newly formed government in Congo. Long story short, after some harrowing events, the threat by Lumumba was terminated, permanently.
The Dominican Republic, 1961
In 1961 the reign of terror imposed by the Dominican Republic dictator Rafael Trujillo came to an abrupt end. The heartless ruler who was guilty of crimes such as ethnic cleansing was ambushed and assassinated. The twist here is that the gunman claimed he was following orders from no person or agency, yet the CIA was openly supportive of the assassin.
South Vietnam, 1963
This was arguably a paid hit by many accounts on behalf of the CIA. The issue with the South Vietnamese leader at that time, Ngo Dinh Diem, was reportedly tenuous at best. It wasn't until plans for a revolt were leaked that the US took action. That action was also swift and deadly, and as we mentioned, to the tune of more than a few dollars and cents too.
In an overthrow so bold that even former US President Lyndon Johnson was reportedly recorded giving orders to do whatever was necessary, Brazilian President Joao Goulart was public enemy number one. The replacement government also fared well and led Brazil into the mid-1980s.
The last recorded country the US has overthrown or played a direct role in regime change was Chile in 1973. It had been three years that the US had been working to remove Chilean President Salvador Allende. The violent leader eventually fell to a military revolt at the hands of military general Augusto Pinochet.