As far as the residency issue is concerned, your mother did NOT have to live with you the entire year and may still be your dependent if she meets all the other requirements. Certain relatives, including mothers, are exempt from the requirement of living with you.
What income did your mom have for 2017? Any income besides Social Security?
My mom only receives social security. She does pay for her half of the rent and her supplemental health insurance. However, I cover the other half of the rent plus ALL of the utility costs, food, and any other miscellaneous expenses.
OK--then her income does not count at all for you to be able to claim her. As Howard1948 said, she can be your dependent even if she did not live with you the whole year.
IRS interview to help determine who can be claimed:
<a rel="nofollow" target="_blank" href="https://www.irs.gov/help/ita/who-can-i-claim-as-a-dependent">https://www.irs.gov/help/ita/who-can-i-claim-as-a-dependent</a>
<a rel="nofollow" target="_blank" href="https://ttlc.intuit.com/questions/3113432-who-can-i-claim-as-my-dependent">https://ttlc.intuit.com/questions/3113432-who-can-i-claim-as-my-dependent</a>
As far as the residency issue is concerned, your mother did NOT have to live with you the entire year and may still be your dependent if she meets all the other requirements. Certain relatives, including mothers, are exempt from the requirement of living with you.