The Walking Dead Season 3 Episode 12

After Rick subdues Morgan who has attacked him, he tries to help Morgan remember who he is by saying that Morgan found him "last year" in Rick's front yard. Although the story's chronology is not synchronized with the series' calendar timeline, surely it has been more a year since Rick last saw Morgan.

*Actually, it is more likely to be slightly less than a year since Rick last saw Morgan. As Judith's parentage is questioned, we can assume that Lori became pregnant around the time Rick found her and Carl. (Again assuming she stopped sleeping with Shane once Rick returned.) Lori gave birth prematurely to Judith, so she would have been pregnant for less than 38 weeks. It also does not appear to have been more than 3 months since Lori's death (considering Judith's growth/development.) So unless Rick wandered for some months before meeting up with Glenn in Atlanta, it would have been nearly a year since Rick last saw Morgan.