How much do I deduct from my employee's pay check for Social Security? I am in McHenry County Illinois if that matters. Thanks.

Go to PaycheckCity.com - Employee Self-Service Tools To Better Manage Your Paycheck.
First you need to register, no charges. It has many useful calculators. If you want to find out what the pay check will be then you can use this link:
PaycheckCity.com - Sign in to use Advanced Features

First select the year and State and then enter your income and deduction info.