The average museum assistant salary at Ontario was $27,887 , which is 11 percent lower than the average salary for this job in California, and 26 percent lower than the national average for this job . Museum Assistant salaries at Ontario typically range from $27,645 to $28,738 (25th to 75th percentile). The highest reported museum assistant salary was $28,942. There are 6 employees at Ontario with the job title museum assistant.