The complete index to St John UCC Church Records, 1870-1986, Smithton, Illinois is now accessible from the St. Clair County (IL) Genealogical Society homepage:
There is also a more detailed baptismal index that distinguishes between the person baptized and the parents or sponsors.
Death records very often specify birthplace and biographical information, valuable data difficult to find elsewhere (yet this attribute is very nearly universal with UCC records in this county!).
A child's birth date appears in Confirmands through 1942, and in Baptisms (nearly 100% coverage). This is significant because vital records registration at the county level only began in late 1877 (but didn't reach 90% compliance until 1916 when a penalty was added to the state law for failure to register).
As with most small town congregations, families are often interrelated. A genealogical clue lacking for one member can often be found in that of a relative!
St. Clair County (IL) Rootsweb Page: http://www.rootsweb.ancestry.com/~ilstclai/stclair.htm