Highest salary at O'fallon Sd 90 in year 2017 was $85,311. Number of employees at O'fallon Sd 90 in year 2017 was 263. Average annual salary was $18,687 and median salary was $15,029. O'fallon Sd 90 average salary is 60 percent lower than USA average and median salary is 65 percent lower than USA median salary.