I was fired from my job and given no reason. I was never written up, never late and never called in sick. Is the legal in MN

Minnesota is an "employment at will" state, which  means that the general rule here is that either the employee or the employer may end their employment relationship at any time, with or without notice, and with or without cause. As with any "general" rule, there are exceptions.  For example, an employer may not fire an employee for an unlawful reason, such as discrimination based on an employee's legally-protected status (of which there are many). Also, if there is a contract between the employer and the employee, then the "at-will" concept does not apply, and the termination must be handled as outlined in the contract. Sometimes, an employer's handbook or other policies may create a contract that controls how a termination is to be handled. So, unless you have a contract or there is evidence that the employer dismissed you for an unlawful reason, the employer's decision to fire you was probably lawful.