Check out this map produced by the League of American Bicyclists and posted on the graphics site Visual.ly. The fonts are small - this image looks intended for a wall, not a computer - but look closely: the darker the state, the larger the share of total trips taken by bicycle, as opposed to driving, walking, or transit; the larger the maroon and yellow box, the larger the number of people commuting to work by bicycle. You can see that California, followed by Florida and New York, have the largest number of bike commuters. But, when you go by mode share - the portion of total trips taken by bike - the leading states appear to be Colorado, Oregon, and (improbably?) Montana. It is hard to tell for sure, but I believe the data came from multiple sources, including the US Census’s American Community Survey.
The map also indicates (in tiny print) the country’s ten cities with the highest mode share for bicycling. Unsurprisingly, Portland ranks first; but I might not have guessed that Minneapolis is second, especially given that city’s notorious winter weather. A larger version of the map contains additional graphics (two excerpted below, with small but readable fonts) that show the total numbers for the top ten cities, as well as some other interesting data, including overall spending on cycling infrastructure.