This data set reports iron (Fe), dissolved organic carbon (DOC), calcium (Ca), magnesium (Mg), potassium (K), phosphorus (P), and aluminum (Al) measured in extractions of soil cores sampled from two boreal peatlands, the S1 and S2 bogs, in the Marcell Experimental Forest (MEF) in Itasca County, Minnesota. The soil cores were sampled on September 2, 2017. Elements were quantified in extractions with hydrochloric acid, sodium dithionite, sodium sulfate, and sodium dithionite plus hydrochloric acid to examine how iron influences carbon and nutrient cycling in peatlands. The S1 and S2 sites are research catchments instrumented for hydrologic monitoring. The S1 bog is also the location of the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment. These data are used, analyzed, and reported in Curtinrich et al. (2021, Ecosystems).