Can I claim my 21 yr old daughter if she's not a full time student?

Yes, you can claim your daughter as a qualifying relative dependent. Dependents can be Qualifying Child or Qualifying Relative. Your daughter doesn't meet the requirements to be claimed as a qualifying child, (since she is over the age of 19 and not a full time student- see the requirement below ) but she meets the requirements to be claimed as a Qualifying relative.

Qualifying child:

• They are related to you.
• They aren't claimed as a dependent by someone else.
• They are a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
• They aren’t filing a joint return with their spouse.
• They are under the age of 19 (or 24 for full-time students).
• No age limit for permanently and totally disabled children.
• They live with you for more than half the year (exceptions apply).

Qualifying relative:

• They don't have to be related to you (despite the name).
• They aren't claimed as a dependent by someone else.
• They are a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
• They aren’t filing a joint return with their spouse.
• They lived with you the entire year.
• They made less than $4,050 in 2017.
• You provided more than half of their financial support. More info

When you add someone as a dependent, we'll ask a series of questions to make sure you can claim them.

Just to clarify one thing too, based on the comment she's not a full time student.
If your daughter was enrolled as a full time student for *any* *one* *semester* that started in the tax year, then she was a full time student in 2017. Note that there is no attendance requirement either. She doesn't have to attend any class for even one single day. She is only required to be *enrolled* as a full time student for any one semester that started in the tax year.
My take on this, is so that it will allow for students enrolled in an accredited online college that does not have a physical campus.

Thank you. I'm not sure but I think the turbo tax system will put her in the ualifying relative for me? And I'm at the end ready to file but haven't yet. Wouldn't I get any credit? I was pretty much supporting her all yr

Seems I'm not getting any credit for that??

What credit are you expecting? The only thing I see you would get for a qualifying relative dependent, is the exclusion of $4,050 of your taxable income from taxation.

I guess I thought it was similar to earned income credit

That's only for a qualify child dependent under the age of 17 on Dec 31 of the tax year.

Ty