Residence and Physical Presence
An applicant is eligible to file if, immediately preceding the filing of the application, he or she:
*
has been lawfully admitted for permanent residence (see preceding section);
*
has resided continuously as a lawful permanent resident in the U.S. for at least 5 years prior to filing with no single absence from the United States of more than one year;
*
has been physically present in the United States for at least 30 months out of the previous five years (absences of more than six months but less than one year shall disrupt the applicant's continuity of residence unless the applicant can establish that he or she did not abandon his or her residence during such period)
has resided within a state or district for at least three months
http://www.uscis.gov/portal/site/uscis/menuitem.5af9bb95919f35e66f614176543f6d1a/?vgnextoid=12e596981298d010VgnVCM10000048f3d6a1RCRD&vgnextchannel=96719c7755cb9010VgnVCM10000045f3d6a1RCRD