The Soundex coding system was created by the federal government in the 1930's and used with the massive Works Progress Administration (WPA) program of indexing valuable historical documents. The first set of documents to be "Soundexed" was the 1880 U.S. Federal census. The second series was the 1900 U.S. Federal census followed by the 1910 and 1920 census. Since then other federal records such as ship passenger lists and military records have been indexed using this system, and today many state and local records are often soundexed.

Soundex holdings:

	SOUNDEX:

	1880	T747	Complete Soundex Indiana

	1900	T1044	Complete Soundex Indiana
	1900	T1047	Complete Soundex Kentucky

	1920	M1560	Complete Soundex Indiana

	CENSUS:

	1920	T625	447	Indiana:	La Porte (part)
			460			Laurence (part)
						Perry (part)
						Pike (part)
						Porter (part)
						Union (part)

			462			Ripley (part)
						Rush (part)
						St. Joseph (part)

			463			St. Joseph (part)

			464			St. Joseph (part)
						Randolph (complete)

			757	Michigan:	Berrien (part)

			758			Berrien (part), Charlevoix,
						Branch (complete)