Ninety-percent of those with surnames as "Washington" are black, according to a recent survey. Only 5% are white.
Using the 2000 census, a survey was conducted among 1,63,036 people with the surname "Washington". 90% of them were found to be African-American.
The reason behind the popularity of the surname, "Washington" among African-Americans is not known. A good guess is that, the surname might have gained popularity, post civil war when blacks were asked to make a choice regarding their surname. "Washington", might have been the preferred choice, symbolic of freedom.