This current study sought to empirically ascertain the influence of combustion temperature on oxide compounds of coconut shell ash (CSA) and compressive strength of CSA-modified concrete. CSA was obtained at combustion temperatures of 500 °C and 700 °C, both at a duration of 2 hours each. The XRF results indicated that the influence of combustion temperature on the oxide compounds of CSA varied. For instance, SiO2 (9.33%) optimized at 700 °C combustion temperature, with 500 °C (9.18%) combustion temperature yielding silica in amorphous form. Also, CaO (5.32%) was optimized at a 500 °C combustion temperature. At age 28 days, 10%CSA@ 500 °C recorded the optimum compressive strength value of 27.80 N/mm2, with compressive strength decreasing to 26.70 N/mm2 when CSA was obtained at a combustion temperature of 700 °C. Thus, for combustion temperatures of 500 °C and 700 °C, the higher the combustion temperature, the lower the compressive strength at ages 7 days and 28 days. Therefore, the optimal combustion temperature for CSA was 500 °C for 2 hours of combustion. Practically, an equation was developed, Y = −0.00002T2 + 0.02T + 23.8, to guide construction practitioners to optimize combustion temperature, CSA oxide compounds, and compressive strength of CSA-modified concrete at age 28 days. The study promotes waste valorization. It has a direct link with combating climate change.