As the construction industry seeks to reduce its carbon footprint, supplementary cementitious materials (SCMs) play a vital role in reducing the clinker content of concrete. This paper synthesizes and comparatively analyze the 365-day compressive strength development of six locally sourced SCMs to establish their long-term performance for use in the Nordic region. The locally sourced SCMs are calcined clay (CC), fly ash (FA), natural pozzolan (NP), electric arc furnace slag (EAFS), oil shale ash (OSA), and ground granulated blast furnace slag (GGBS). A total of 31 concrete mixes were evaluated, with SCMs replacing cement at levels from 15% to 60%. While all SCM mixes exhibited lower early-age strength than the Portland cement reference, long-term strength was significantly enhanced. The most promising results include 15% FA (102 MPa), 35% NP (99.5 MPa), and 45% GGBS (96.5 MPa) at 365 days. High-volume replacement was also proven viable, with 35% oil shale ash matching the reference strength. The findings demonstrate that these regionally available SCMs offer a viable pathway towards producing high-performance concrete with significantly reduced clinker content, suitable for a wide range of structural applications.