The e-mail was time stamped at about 2:30 this afternoon and was sent to everyone at the sheriff's office.
In that email, Sheriff Williams says he is in the process of informing the governor as required by state statute.
His final day will be May 23, which is in less than a month.
He says the decision was not made in haste or without considerable deliberation.
According to the email, Sheriff Williams says an opportunity in the private sector is one that may never come again.
However, he did not elaborate on where that job opportunity is.
The Vanderburgh County Democratic Party Chairman has also been notified of Williams' departure.
Williams was elected Sheriff in 2007, and has spent the last 7 years as the county's top cop.
The democrat has held every rank in his 20-year career at the sheriff's office.
The democratic party will now have to name Williams' successor.
Williams has confirmed with Eyewitness News of his retirement.