To establish the statistical behavior of ionospheric TEC variations from high latitudes to mid‐latitudes during the main and recovery phases of geomagnetic storms, we conducted a superposed epoch analysis of interplanetary magnetic field, solar wind, geomagnetic indices (AE and SYM‐H), and global navigation satellite system (GNSS)‐total electron content (TEC) data for 20 yr (2000–2019). In this study, we identify 663 geomagnetic storm events with the minimum SYM‐H value of less than −40 nT and investigate the characteristics of the TEC variations for the weak (−60 ≤ SYM‐H_min < −40 nT), moderate (−100 ≤ SYM‐H_min < −60 nT), and strong (−150 ≤ SYM‐H_min < −100 nT) geomagnetic storms. The main results obtained from the present study are as follows: (a) The TEC enhancements related to the tongue of ionization (TOI), auroral oval, and storm‐enhanced density (SED) plume are more dominant in winter than in summer during the main phase of geomagnetic storms. (b) The structure of the mid‐latitude trough in the nighttime sector becomes unclear in winter. (c) The TEC depletion at auroral and mid‐latitudes (40°–70° GMLAT: geomagnetic latitude) starts to appear in the morning sector (8–10 hr GMLT: geomagnetic local time) during the main phase of geomagnetic storms and the decreased region extends in the lower latitude and GMLT directions with time. The negative storm activity tends to be enhanced significantly as the storm intensity becomes larger. The activity of the TEC depletion is dominant in summer than in winter, which is agreement with the classical ionospheric storm scenario.