Soils have a large carbon storage capacity and sequestering additional carbon in agricultural fields can reduce CO2 levels in the atmosphere, helping to mitigate climate change. Efforts are underway to incentivize agricultural producers to increase soil organic carbon (SOC) stocks in their fields using various conservation practices.  These practices and the increased SOC provide important additional benefits including improved soil health, water quality and – in some cases – biodiversity. Many current initiatives offer only a relatively modest payment per acre with little or no field validation of actual SOC sequestered.  This is due to the concern that measuring actual SOC change accurately in farm fields is impractical and uneconomical.  However, if agricultural producers are to receive adequate compensation for their carbon sequestering efforts, baseline soil carbon inventories and follow-up measurement and verification are needed.  In late 2021 an intensive soil measurement project was conducted on four 16 ha fields in the US Midwest.  This project included collecting lab-analyzed soil samples to depths of 90 cm and 30 cm on .4 ha and .1 ha grids respectively, and soil sensor profiling technology that included NIR, EC, and compaction sensing. In all, 184 0-90 cm sensor probe investigations were completed and over 1200 lab samples were analyzed. The objectives of the project were to: 1) Create a high quality, lab-analyzed SOC baseline that could be used to evaluate SOC measurement and modeling approaches, 2) Evaluate the extensive lab sample dataset to improve understanding of lab estimations of field SOC, bulk density, and soil profile SOC, and 3) Evaluate the performance of sensor probe technology including using sensors to estimate SOC at unsampled locations. Results of the project reveal important considerations for measuring bulk density, lab-analyzed sample repeatability, and soil sensor calibration methods.