The soybean variety DLL0840 is disclosed. The invention relates to seeds, plants, plant cells, plant tissue, harvested products and soybean lint as well as to hybrid soybean plants and seeds obtained by repeatedly crossing plants of variety DLL0840 with other plants. The invention also relates to plants and varieties produced by the method of essential derivation from plants of DLL0840 and to plants of DLL0840 reproduced by vegetative methods, including but not limited to tissue culture of regenerable cells or tissue from DLL0840.