Journey into Mystery volume 1 Continues into Thor vol.1 with issue 126.
Journey into Mystery volume 1 was a comic that began publication in 1952 by Atlas, and although it wasn't until the eighty-third issue that Thor even appeared in comics, let alone the title, it is most often linked to his character. This is why after releasing the one hundred and twenty-fifth issue of the series in 1966 that the series changed its name to become the first volume entitled Thor volume 1. For more than three hundred issues the title remained as Thor, but in 1996 after the five hundred and second issue of the series, they decided to change the name back to Journey into Mystery (vol.3) which is what it was called up until its end in 1998 with the five hundred and twenty-first issue. Although these later Journey into Mystery issues (503-521) spin out of Thor vol.1, they are not counted in the collective Thor series.
Back in 1998, Thor's adventures restarted in the first issue of Thor volume 2 and there they were contained until issue eighty-five when the series concluded because of Avengers: Disassembled in 2004. After that event Thor disappeared for a couple years until he returned in 2007 for his newest volume, Thor volume 3, which only lasted for twelve issues with its restarted numbering. After that Marvel realized it had now published 599 comics in the collectively-grouped "Thor" series (even though eighty-two issues had nothing to do with him) and therefore reverted the numbering back to its original formation and thus, the 600th issue and the succeeding issues were born.