If my child left In July 2020 for the army can I still claim her

[MaryK4]

It depends- if she was under 19 and she did not provide more than one half of her support for the year.  See the link below for all the qualifications.  

Rules for Claiming a Dependent on Your Tax Return - TurboTax

[Hal_Al]

Yes, probably, particularly is she was still in school (incl high school)  prior to leaving.

A child of a taxpayer can still be a “Qualifying Child” (QC) dependent, regardless of his/her income, if:

1. He is under age 19, or under 24 if a full time student for at least 5 months of the year, or is totally & permanently disabled
2. He did not provide more than 1/2 his own support. Scholarships are considered third party support and not as support provided by the student.
3. He lived with the parent (including temporary absences such as military training) for more than half the year. When a military member is taking basic and advanced training, they are still considered as living at home until they get their permanent duty station, for purposes of this rule

So, it doesn't matter how much he earned. What matters is how much he spent on support. Money he put into savings does not count as support he spent on him self.

The support value of the home, provided by the parent, is the fair market rental value of the home plus utilities & other expenses divided by the number of occupants.

The IRS has a worksheet that can be used to help with the support calculation. See: http://apps.irs.gov/app/vita/content/globalmedia/teacher/worksheet_for_determining_support_4012.pdf

Furthermore, there is a rule that says IF somebody else CAN claim him as a dependent, he is not allowed to claim himself. If he has sufficient income (usually more than $12,400), he can & should still file taxes. In TurboTax, he indicates that somebody else can claim him as a dependent, at the personal information section.  TT will check that box on form 1040.

Even if he had less, he is allowed to file if he needs to get back income tax withholding. He cannot get back social security or Medicare tax withholding.

[Hal_Al]

@MaryK4  said "she may be better off if you do not claim her".  That's particularly important for 2020, because she will be eligible for the $1800 stimulus / rebate credit.

Under the CARES Act, if she is claimed, or qualify to be claimed, as a dependent on someone else’s 2019 return she did not receive a stimulus check, in 2020.   If she qualified as a dependent for 2019, but will not be for 2020, she will most likely get it in 2021, when she files a 2020 tax return.