Can a parent claim their 21 yr old dependent who is totally supported by parents on their taxes if that dependent made more than $3500.00 that year. They are not a student.

No. They cannot claim that child as a dependent as that child earned more than the allowable minimum and must file their own income taxes.

Is this because the dependent is 21 or because of the amount they made?? I have a 19 yr old and an 18 yr old at home, both have made over the amount stated prior but they are totally supported by their father and me. Can we claim them on our taxes?

No. If they earn in excess of the allowable minimum you can't. If you do claim all 3 kids, the IRS will catch the "mistake" on your part and expect the money paid to you to be returned.

Is this because the dependent is 21 or because of the amount they made??? I have a 19 yr old and an 18 yr old at home, both have made over the amount stated prior but they are totally supported by their father and me. Can we claim them on our taxes??

It's a combination of things. To be your dependent your son or daughter must be either a qualifying child or a qualifying relative. To be a qualifying child he/she must be either (a) under age 19 or (b) age under 24 and a full time student. Hence your 21-year old does not meet this test and so is not considered to be a qualifying child. To be classified as a qualifying relative your child must have income less than $3500. Because your 21-year old made more than $3500, s/he is not a qualifying relative. Since s/he is neither a qualifying child nor a qualifying relative you can not claim him/her as a dependent.

As for your other children - the 18-year old is definitely a qualifying chid. Your 19-year old may be, if s/he is either a full time student or made less than $3500.

IRS Pub 501 spells out all the gory details, starting on page 11:

http://www.irs.gov/pub/irs-pdf/p501.pdf