Can I move to Ohio from Colorado with my 18 month old legally?

If there are no court orders in effect that allocate parental responsibilities and establish specific parenting time rights, there is nothing to prevent you from moving to wherever you want, whenever you want. However, if the father doesn't like your decision he can begin a court action to establish specific rights and that will be possible in Colorado even if you are gone. Depending on the actual history of the child's relationship with the child and all the relevant facts, the Colorado court could legally require you to return the child to Colorado. You need to think seriously about what is best for the child and try to get things resolved in court before you move because it will be much easier to do it now rather than later. You should consult a lawyer to learn more about your options and reasonable expectations.