The state of Illinois now has a Civil War Muster and Descriptive Rolls Database available at http://www.sos.state.il.us/departments/archives/datcivil.html . The direct link for searching the database is at http://www.ilsos.gov/genealogy/ .
You can search the database by the veteran’s name/partial name (you must enter at least two letters of the surname), company, unit, or place of residence. I did a search for smi . I got over 500 results (the maximum number of results you can get is 500) so I tried again, this time with owen . This time I got 284 results, covering both Owen and Owens.
Results are provided in a table showing name, rank, company, unit, and residence. (Be sure to check the ranks abbreviation list if you’re not clear on what a MUS or a UCOOK is.) Click on the name of the solider and you’ll get a page with additional personal information (eye and hair color, height, occupation, etc) as well as service information (muster in date, where they joined, when mustered out, etc.) There’s also a additional section which contains additional notes (I saw remuster dates, discharge for disability notes, death information, etc.)
The database was very quick to search but occasionally it seemed to hiccup in its searching, and I had to back all the way out to the top page and try again. This might have been just a Firefox issue.