Guide to Soundex codes

Code   Letters
1          B, P, F, V
2          C, S, K, G, J, Q, X, Z
3          D, T
4          L
5          M, N
6          R

The letters a, e, i, o, u, y, w, and h are not coded.
The first letter of the surname is not coded.
Every Soundex number is a 3-digit number.
A name with no code numbers, as Lee, would be L000.
A name with only one code number would have two zeros, (Kuhne), would be K500.
A name with two code numbers would have one zero added, Ebell = E140.
No more than three digits are used, so Reynolds = R543, not R5432.

When double letters appear in a name or one letter immediately follows or precedes an equivalent, the two are coded as one letter.
Some Soundex Examples:
Kelly = K400
Lloyd = L300
Schaefer = S160
Icenogle = I252
Coleman = C455
Marable = M614
Adams = A352
Barnes = B652
Zimmerman = Z565
Raymond = R553
Cooley = C400

When several surnames have the same Soundex code, the cards are in alphabetical order by given name

Prefixes like “van,” “Von,” Di,” “De,” “Le,” “D,” “Dela,” or “Du” are sometimes disregarded in alphabetizing and coding.

Only census years 1880, 1900, 1910 and 1920 have been soundexed.

In 1880 only those households with children aged 10 or under are soundexed.

In 1910, Soundex or Miracode was created for 21 states. Louisiana uses both and the other states are indexed with either Soundex or Miracode.  The method used is noted at the beginning of the State listing.   States included in the Soundex/Miracode are: AL, AR, CA, FL, GA, IL, KS, KY, LA, MI, MS, MO, NC, OH, OK, PA, SC, TN, TX, VA, WV.

There is more to the Soundex system than the few items I've outlined here.  You may be able to get more information at your local library or Family History Center. Heritage Quest is one online source for Soundex and census records.