Churches and homes throughout the southern Arizona city rang bells at 10:11 a.m. MST, the exact time the gunman shot Giffords and methodically moved down a line of people waiting to meet her during a congressional meet-and-greet on Jan. 8, 2011.
Saturday, Giffords' husband, former astronaut Mark Kelly posted a photo via Twitter, showing Giffords returning to the parking spot she chose on the day of the shooting.
Friday, the congresswoman participated in a ceremony honoring her late staff member, Gabe Zimmerman, who died in the rampage.
Six people were killed, including a 9-year-old girl born on 9/11 and a federal judge. Thirteen others were shot, including Giffords.
The 41-year-old congresswoman has spent the last year in Houston undergoing intensive physical and speech therapy.
Doctors and family members have called her recovery miraculous after the shooting. She is able to walk and talk, vote in Congress and gave a televised interview to ABC's Diane Sawyer in May.
However, doctors have said it would take many more months to determine the lasting effects of her brain injury. The three-term congresswoman has four months to decide whether to seek re-election.
Giffords and Kelly are planning to join thousands at an evening candlelight vigil at the University of Arizona. Kelly was expected to speak.
Jared Lee Loughner, 23, has pleaded not guilty to 49 charges in the shooting. Loughner, who has been diagnosed with bipolar disorder, is being forcibly medicated at a Missouri prison facility in an effort to make him mentally ready for trial.
The Associated Press contributed to this report.