According to Official Guinness Records,
The USA won a record 239 medals at the third Olympic Games, held in St Louis, Missouri, USA, in 1904. The record haul consisted of 78 gold, 82 silver and 79 bronze medals.
USSR lies in second place with a total of 195 medals (80 gold, 69 silver, 46 bronze) won at the 1980 Games held in Moscow, USSR. Third place goes to Great Britain, whose athletes picked up 145 medals (56 gold, 51 silver, 38 bronze) in the 1908 Games in London, UK.
For a complete list of 1904 records, please visit 1904 Guinness Records in United States.