In my post GMs by Federation I counted 68 American GMs. While catching up on the last few months of Chess Life, I noticed that the April 2008 issue included a list of American GMs in the '2007 Yearbook'. The Wikipedia and CL lists compare very well.
All but two of the 61 names on the CL list are on the Wikipedia list. The two exceptions -- Susan Polgar and Gennadi Zaichik -- are on Wikipedia under other nationalities. This indicates that the Wikipedia list is not consistent in how it lists a GM's nationality.
The CL list doesn't include the names of nine deceased American GMs, all of whom are listed in Wikipedia with date of death. A 10th GM, listed with date of death, is on CL's active list. That player is 'Fischer, Bobby', who died 17 January 2008, a few weeks after the CL yearbook ('current as of 31 December 2007') was compiled .