You can see a full list of all the wind farms in the USA here. The total number does not seem to be given on the internet, probably because new ones are always being added and some older ones go out of action, but you can get a general idea from the list.
The number of large wind farms (160 megawatts or more) was 105 at the end of 2011. Of course there are a good many small wind farms as well which may not always show up on a list. The largest wind farm in the country is the Roscoe farm in Texas at 780 MW, which was formerly the largest in the world (in 2012 a larger one was built in the UK). However, an even larger farm is expected to be built in Nebrask in the next few years; in fact about 20 new wind farms are proposed or under construction in the US, so any list will have to be regularly updated.