My fiance is in The Air Force 250 miles away. My child custody agreement says I can't move out of the county I live in or the surrounding counties. tx

Without additional facts, it is almost impossible to estimate the likelihood of the court allowing you to move.  The overriding consideration is "the best interests of the child."   You will have to file a motion to modify the custody order.  Although there isn't a single determinative factor, the court will look at whether dad has exercised all or most of his periods of possession, whether he is current on child support, the age of your child, do name just a few.   Of course, if you and Dad reach an agreement regarding lifting or changing the geographic restriction, then you could enter the agreed modification.  At a minimum, you will probably want to talk to an attorney in your county about your options.  It may be beneficial to talk to one who has experience with military issues.