Highest salary at O'fallon Sd 90 in year 2018 was $88,303. Number of employees at O'fallon Sd 90 in year 2018 was 306. Average annual salary was $16,755 and median salary was $13,271. O'fallon Sd 90 average salary is 64 percent lower than USA average and median salary is 69 percent lower than USA median salary.