How can I serve as a volunteer with the Illinois Department of Corrections? 35. What's the difference between a jail and a prison?You can be arrested if a law enforcement officer has probable cause to believe that you committed an offense. Illinois law provides that a felony is any offense for which the penalty is one year of imprisonment or more. The arrest may be made with or without a warrant, depending on the circumstances. Misdemeanor crimes carry a possible jail sentence of less than one year. You need your criminal record to figure out which offenses on your criminal record can be expunged (erased) and which can be sealed (hidden). Detainment vs. arrest. Below, we're going to explain the difference between these two processes and your rights during each one. When an officer can articulate why they believe you could be involved in a crime, they can detain you.