1st meridian may refer to:
1st meridian east, a line of longitude east of the Greenwich Meridian 1st meridian west, a line of longitude west of the Greenwich Meridian First principal meridian in Ohio and Indiana, United States, 84°48'50" west of Greenwich Principal meridian of the Dominion Land Survey in Canada, 97°27′28.41″ west of Greenwich Counter Revolutionary Warfare Unit a.k.a. First Meridian Squadron, a former special forces unit in the Fijian military
See also Meridian 1, a Russian communications satellite