A felony remains on your criminal record forever. Employers will often perform an entire criminal background check on you, so when asked if you've ever even convicted of a felony, you must always answer honestly and explain the circumstances because they will discover it.
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I'm not aware of anything that limits employers in regards to background checks. If you authorize them to do a background check but you try to limit them to a certain time frame you'll make them suspicious. Department of Justice would be the prefererred source for criminal records and it's my undersdtanding that they keep records for 100 years.