Did the US Congress ever officially declare war on North Korea?

The UN became a war combatant itself after North Korea invaded South Korea on 25 June 1950 (see Korean War). The UN Security Council condemned the North Korean action by a 9-0 resolution (with the Soviet Union absent) and called upon its member nations to come to the aid of South Korea. The United States and 15 other nations formed a "UN force" to pursue this action. In a press conference on 29 June 1950, U.S. President Harry S. Truman characterized these hostilities as not being a "war" but a "police action".

So no, the US never officially declared war on North Korea. Infact the United States has not officially been to war since World War II, which is the last time Congress declared war.