Helpful Clues in the Census
Beginning in the 1900-1930 Census Records, naturalization information began to be documented in the Census. Year of Naturalization is given in the 1920 Census. Using the "Soundex Code" may make it easier for you. This system was developed so that you can find a surname even though it may have been recorded under various spellings. To search for a particular surname, you must first work out its code:

Basic Soundex Coding Rule:
Every soundex code consists of a letter and 3 numbers, such
as W-252. The letter is always the first letter of the surname. The
numbers are assigned to the remaining letters of the surname
according to the soundex guide shown below. Zeroes are added
at the end if necessary to produce a 4-character code.
Additional letters are disregarded. Examples:
-WASHINGTON is coded W-252 (W, 2 for the S, 5 for the N,
2 for the G, remaining letters disregarded)
-LEE is coded L-000 (L, 000 added) Basic Coding Guide:
Number Represents the Letters
1 B,F,P,V
2 C,G,J,K,Q,S,X,Z
3 D,T
4 L
5 M,N
6 R
Disregard the letters A,E,I,O,U,H,W and Y

Abbreviations used in the Citizenship column of census records:
AL=Alien; NA=Naturalization
NR="Not" Reported
DI ="First" Papers Filed