These are medalists not medals. That means Michael Phelps counts as only one gold medalist for Maryland, because that was the single highest Olympic honor he received.
Wondering how we derived these numbers? We scraped Wikipedia data in the "U.S. Gold Medalists", "U.S. Silver Medalists", and "U.S. Bronze Medalists" categories, removed duplicates (taking the person's highest honor as their category), searched the person's attributes for their birthplace while falling back on a text search, then tallied them by state. Overall, about two thirds of the athletes listed on Wikipedia had birth places that we could interpret. The list here is static, updated August 8th, 2012. State populations were estimated based on U.S. Census data. We do not claim ownership of this information or guarantee its accuracy. So don't go and do something rash with it, like invade California.