Integrated energy systems have attracted ample attention due to the fact that they increase the efficiency of the system and consequently reduce the environmental impacts. Among integrated energy systems, integration of a gas turbine (GT) with a multi-effect desalination (MED) and an organic Rankine cycle (ORC) has introduced itself as a potential option. In this paper, a comprehensive thermodynamic modeling of an integrated system consisting of a micro gas turbine, a single pressure heat recovery steam generator (HRSG), an ORC and an MED is conducted. Exergy and economic analyses are performed. In addition, a multi-objective optimization is performed to determine optimized design parameters. Moreover, an optimization is performed for different working fluids including R123, R134a and R245fa. The distilled water production and the total cost rate (power generation price) are considered as two objective functions. The fast and elitist Non-dominated Sorting Genetic Algorithm II (NSGA-II) is applied to optimize the objective functions simultaneously. The results show that MED evaporator approach temperature has a significant effect on the optimum selected power and distilled water capacity. Furthermore, by increasing compressor pressure ratio, the exergy efficiency increases and the cost rate decreases. Moreover, R134a shows the best exergy efficiency compared with other fluids. (C) 2016 Elsevier B.V. All rights reserved.