The color-magnitude diagram (CMD) is the most powerful tool to derive quantitative star formation histories (SFHs) of complex stellar systems which host populations with different ages and chemical compositions. We present some results from the LCID project, based on the analysis of deep HST/ACS CMDs reaching the oldest Main Sequence (MS) Turn Off (TO) to derive the SFH of isolated dwarf galaxies of the Local Group (LG). In particular, we focus on Tucana, one of the few isolated dwarf spheroidal galaxies. The method applied for this work relies on the packages IAC-star and IAC-pop. A few aspects of the quantitative estimate of SFHs using this method are presented and discussed.