Where was the microwave oven invented?

Percy Spencer, the engineer who came up with the idea for the microwave oven, was working for Raytheon Company in Waltham, Massachusetts, at the time he got the idea.

This device, which Raytheon patented on October 8, 1945, appeared in 1947. The "Radarange" was a monster; it was about six feet tall and weighed over 700 pounds.

Further information: Percy LeBaron Spencer is considered to be the inventor of the microwave oven. He was working as an engineer with the Raytheon company when he was experimenting with and testing a magnetron. The magnetron had already been invented during WWII and allowed the Allies to determine the exact locations of Nazi war machines and arsenals, as the magnetron produced microwaves which radar then bounced off the arsenals, and back to the Allies. It was while testing the magnetron following the war, that Dr Spencer reached into his pocket for his chocolate bar, and discovered it had completely melted. He made the connection between the melted chocolate and the heat-producing magnetron, and tested his theory on a bag of unpopped corn kernels, which then popped. Next, he placed an egg in front of the magnetron. The egg exploded.

Dr Spencer is therefore credited with discovering one of the critical components of the microwave oven. Development of the microwave oven grew out of his observations, and by 1947 a commercial oven was being sold by Raytheon.