Write in vote

In order for it to count that person has have collected a certain amount of signatures (usually 500) from legal registered voters from his county seat (and sometimes neighboring county seats or their state depending on the position). These people cannot have voted in the primary election or their signature is discounted (marked off). Susu

In order for your vote to count, that person that you write in has to register as a write-in candidate. As SuSu stated, sometimes there are signature requirements, but sometimes there aren't. It all depends on the level of office that they are running for. So if you write in Mickey Mouse for President, I doubt it will count!