I am legally married, but separated for 5 years. We have lived apart for 5 years. My Mom also lives with me. She does not have an income. Can I file single?

[jerry2000]

No, you can not file as single.
If you were legally married as of 12/31/2015, your choices are Married Filing Jointly, if your spouse agrees,  or Married Filing Separately, unless you meet the qualifications to be "considered unmarried", in which case you could file as Head of Household. The requirements are:

Considered Unmarried
To qualify for head of household status, you must be either unmarried or considered unmarried on the last day of the year. You are considered unmarried on the last day of the tax year if you meet all the following tests

1. You file a separate return

2. You paid more than half the cost of keeping up your home for the tax year.

3. Your spouse did not live in your home during the last 6 months of the tax year. Your
spouse is considered to live in your home even if he or she is temporarily absent due to special circumstances.

4. Your home was the main home of your child, stepchild, or foster child for more than half the year.

5. You must be able to claim an exemption for the child. (There are some exceptions to this rule, see IRS Pub 17, Chapter 2 and 3) You can find Pub 17 at this link
http://www.irs.gov/pub/irs-pdf/p17.pdf

[sherrondickenson]

Turbo Tax guided me last year to file single, because I did live apart from my husband all year, and, my mother was a qualifying dependent? I paid all of the cost in my home separate from my husband.