I only have $4000 in my 401k, and was recently laid-off. I need the money to start a small business. How much can I expect to get after taxes. Are there state tax penalties for Florida?

You'd probably see less that $3K

Cashing in your 401K will instantly incur a penalty of 20% of your funds plus you will have to pay taxes on the original $4000. Not knowing your tax rate but using a Federal tax rate of 15%, you may clear about $2600. Be better if you keep the money in the 401K.

Cashing in your 401K will instantly incur a penalty of 20% of your funds plus you will have to pay taxes on the original $4000. Not knowing your tax rate but using a Federal tax rate of 15%, you may clear about $2600. Be better if you keep the money in the 401K.
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Yes, you are right, it is 10% penalty. Still better to keep the funds in the 401K.

Let's summarize: The bottom line is 10% penalty only applies to those age less than 59 1/2. Otherwise, 10% penalty does not apply to those older than 59 1/2. The 10% penalty is on top of the income tax that you have to pay. For example for age younger than 59 1/2 (which I assume you are), than you need to pay $400 from the original $4k. Then your $4k is being added to you total earned income and pay tax on it. Your tax amount will based on your income tax bracket. Florida does not have state tax so you don't need to worry about paying state tax. You just need to take care of Uncle Sam.