Your short answer is:  possibly.  A longer answer requires a review of the relevant section of Missouri state tax law.

In Missouri, depending on your income and filing status (Single, Married Filing Jointly, etc.) taxpayers are potentially able to exclude all, or at least some portion, of their retirement pension income.  This also applies to Social Security benefits.  The rules themselves can be complicated, but the Missouri Department of Revenue has published a helpful chart to assist taxpayers in determining if they are eligible for this state tax benefit.  Here is a courtesy link to that document:

http://dor.mo.gov/pdf/pension.pdf

A brief (written) explanation of the pension deduction benefit is outlined further on this MO Dept. of Revenue webpage:

http://dor.mo.gov/personal/ptc/pension.php

That said, a complete, 100% accurate, determination of whether or not you can exclude some (or all) of your civil service pension would require going through the math of the Missouri state tax forms.  In other words, we won't know for sure how much, if any, of your pension can be excluded without actually going through the act of filling out and completing a Missouri tax return.

There is "no one size fits all" response that accurately describes every Missouri taxpayer, because under the Missouri rules, a state-level pension exclusion depends on the individual circumstances.  This is unlike some other states, for example, which flatly exclude federal government pensions from all state taxation.  Missouri, on the other hand, taxes some but not others.  However, the pension flowchart (linked above) should give you a good idea if you qualify for an exclusion, or not.

Thank you for asking this important question.