The Collaborative International Dictionary of English v.0.48:

White person \White person\
   A person of the Caucasian race (--6 Fed. Rep. 256).

   Note: In the time of slavery in the United States white
         person was generally construed as a person without
         admixture of colored blood. In various statutes and
         decisions in different States since 1865 white person
         is construed as in effect (as of 1913): one not having
         any negro blood (Ark., Okla.); one having less than one
         eighth of negro blood (Ala., Fla., Ga., Ind., Ky., Md.,
         Minn., Miss., Mo., N.C., S.C., Tenn., Tex.); one having
         less than one fourth (Mich., Neb., Ore., Va.); one
         having less than one half (Ohio). Since the passage of
         civil rights legislation in the 1960's and 1970's, the
         term has little legal significance -- for some
         purposes, as in filling out questionnaires, a person's
         race is whatever the person claims it to be.
         [Webster 1913 Suppl. +PJC]

WordNet (r) 3.0 (2006):

White person
    n 1: a member of the Caucasoid race [syn: White, White
         person, Caucasian]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

WHITE PERSONS. The acts of congress which authorize the naturalization of
aliens, confine the description of such aliens to free white persons.
     2. This of course excludes the African race when pure, but it is not
easy to say what shade of color or mixture of blood will make a white
person.
     3. The constitution of Pennsylvania, as amended, confines the right of
citizenship to free white persons; and these words, white persons, or
similar words, are used in most of the constitutions of the southern states,
in describing the electors.