This paper applies the logarithmic mean divisia index to explore the decomposition and decoupling of sectoral carbon emissions across four provinces in the Yangtze River Delta (YRD). The results show that (1) the YRD experienced a significant upward trend in sectoral carbon emissions, among which Anhui and Jiangsu provinces experienced the largest increase in carbon emissions. (2) Anhui and Jiangsu showed expansive coupling or weak decoupling in the “10th Five-Year Plan (FYP)”, and Shanghai and Zhejiang indicated weak decoupling and strong decoupling in the “11th FYP”, “12th FYP”, and “13th FYP”. These observations show that the YRD has been transforming its economic growth patterns and increasingly concentrating on the green economy. (3) Shanghai was the most progressive in decoupling. An inspection of decoupling indicators reveals that declining energy intensity contributed most to decoupling, whereas the population scale was less important. In addition, the industry structure and energy structure varied among the provinces.