The ionosphere is a layer of atmosphere 60 km to 1100 km above the earth and is composed of solar raysand ionized gases. The ionosphere is an important layer affecting Global Navigation Satellite System (GNSS) measures.The quality of GNSS measures is directly related to the changes in the ionosphere. For this reason, monitoring changes inthe ionosphere is quite important. One of the important parameters expressing the characteristic of the ionosphere is theTotal Electron Content (TEC), which is a function of electron density exhibiting transformation with solar radiation.In this study, 68 stations including 56 Continuously Operating Reference Stations-Turkey (CORS-TR) stations andalso IGS stations were taken for evaluation. Bernese v5.2 GNSS software developed by Bern University of Switzerlandwas employed at the evaluation stage. From 2009 until 2015, TEC values were calculated at two hourly intervals, one dayfor each month. In the study, where a Single Layer Model was used, TEC values obtained from GNSS measurementshave been compared with the TEC (IRI-2012 TEC) values obtained from the global ionosphere map (GIM-TEC) and theinternational ionosphere reference model programme published by the Centre for Orbit Determination in Europe(CODE), the European Space Agency (ESA), and the Jet Propulsion Laboratory (JPL). As a result, the regional (RIM)TEC values and the global (CODE, ESA, JPL) TEC values showed a large similarity, and the IRI obtained TEC valuesremained lower than these four values was observed. Correlation coefficient was calculated to determine the relationshipbetween regional TEC values obtained after the evaluation and global TEC values. There is a positive and quite highcorrelation between the regional (RIM) TEC values produced by the calculated correlation coefficients and the global(CODE, ESA, JPL) TEC and IRI TEC values.