O’Fallon Historical Society has free, online genealogy collections including:

• O’Fallon Obituary and Marriage Index 1898-2007

• O’Fallon School Photos | Class Photos

• O’Fallon History 1954 at Internet Archive

They also have these historical pages

• O’Fallon Society News

• O’Fallon Coal Exhibit

• O’Fallon Cemetery Detectives