From a previous marriage I have 3 daughters. I asked my ex-wife to let me claim my youngest especially since I'm paying child support. She said no because she is on Medicaid and if I claim her then she will loose her Medicaid benefits for all the girls. Is that true? Also I need a good lawyer in NC to help me with joint custody as well?

With all the changes in Tax law coming into effect last week, your best bet for a correct answer will be a tax preparer in your local area. Medicaid here (I'm in eastern NC myself) is in such disarray that any two people will give you three correct answers that contradict each other. There are several databases and referral sources for attorneys but the tried and true method is to spend a day in family court to see how the clerks treat the attorney. Judges have to deal with all of them, clerks don't have to be nice to butthats.

When claiming a child, the amount of support you provide usually doesn't matter. Instead, to qualify as a dependent, the child must not provide more than 1 / 2 of his or her own support for the year.
However, the child must live with you more than 1 / to the year. So, the child of divorced or separated parents is usually the qualifying child of the custodial parent.
However, the child can be the qualifying child of the noncustodial parent if all of these are true:

• One or both parents provided more than 1 / 2 the child's total support for the year.
• One or both parents have custody of the child for more than 1 / 2 of the year.
• The parents are divorced, legally separated, or lived apart at all times during the last 6 months of the year.

In the above situation, the noncustodial parent can take the dependency exemption if 1 of these is true:

• The custodial parent gives up the exemption by signing a Form 8332: Release / Revocation of Release of Claim to Exemption for Child by Custodial Parent. The noncustodial parent must attach the Form 8332 to the return.
• A pre-1985 agreement says that the noncustodial parent can claim the exemption. The noncustodial parent has provided at least $600 of the child's support.
• The noncustodial parent attaches to the return certain pages of an agreement that took effect from 1985–2008. The agreement must say:
  
  • That the noncustodial parent can claim the child
  • Which years the noncustodial parent can claim the child
  • That the custodial parent won't claim the child for those years

I'm suspicious of her claim. Sounds to me like she isn't reporting your support amount on her Medicaid forms due every 6 months.

The rule of thumb here is that the person that provides more than half the support of a minor child can claim that child as a dependent. IRS Publication 501 Publication 501 (2013), Exemptions, Standard Deduction, and Filing Information has the rules on what qualifies a dependent.

So the amount of support you pay may be a factor. You don't need permission to claim a child IF that child qualifies under the IRS regs.