Coles County, IL Genweb Project a collection of online resources for genealogy researchers
City of Mattoon (Coles County) Death Certificate Registers Index, 1899-1918
Census-Online.com - census transcriptions for Coles Co.
Coles County Surnames
Illinois Public Domain Land Tract Sales Database - for Coles County select this county and then enter the surname (at least first 2 letters) of the person whom you wish to search on  (a government database of over 550,000 19thC land sales in Illinois - info on obtaining original copies is here )
Genealogy Trails History and Genealogy Project - Pages for This County you will find user contributed records of births, deaths, marriages, military and newspaper extracts at this site
Interment.net - cemeteries for Coles County
Mattoon Court of Common Pleas Case Files Index (1869-1873)
The Tombstone Transcription Project - cemeteries for Coles Co. IL
US GenWeb Archives for Coles County cemeteries, newspapers, wills, military rosters etc recorded online

Additional Resources

Ilinois Newspaper Search enter your ancestor's name to instantly search the world's largest newspaper archive; over 12 million newspaper pages
Illinois Birth Records
Illinois Marriage Records
Illinois Divorce Records
Illinois Death Records