This paper reports spatial and temporal changes at the regional level in soil organic carbon (SOC) using a soil‐test database. A total of 23 329 SOC test values recorded between 1990 and 2004 by certified commercial laboratories and collected in a mountainous French region (Franche‐Comté) were integrated in a database. Results show a strong trend in organic carbon content, mainly related to elevation. A large loss in SOC was observed over the survey period. This loss correlated with baseline SOC content with greater loss from soils with higher carbon content. This loss is likely to be due to both changes in land use from permanent grassland to cultivation and to an increase in temperature during the survey period. Our study demonstrates that past soil‐test results which were not originally intended for monitoring can provide an alternative method for detecting changes in SOC.