Molecular interactions in 1-butanol + ionic liquid (IL) solutions have been investigated by measuring and modeling activity-coefficient data. The activity coefficients in binary solutions containing 1-butanol and an IL were determined experimentally: the ILs studied were 1-decyl-3-methyl-imidazoliurn tetracyanoborate ([Im(10.1)]+[tcb](-)), 4-decyl-4-methyl-morpholinium tetracyanoborate ([Mo-10.1](+)[tcb](-)), 1-decyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide ([Mo-10.1](+)[ntf(2)](-)), and 4-decyl-4-methyl-morpholinium bis(trifluoromethylsulfonyl)imide ([Mo-10.1](+)[ntf(2)] (-)). The methods used to determine the activity coefficients included vapor-pressure osmometry, headspace-gas chromatography, and gas-liquid chromatography. The results from all of these techniques were combined to obtain activity-coefficient data over the entire IL concentration range, and the ion-specific interactions of the Its investigated were identified with 1-butanol. The highest (1-butanol) IL interactions of the ILs considered in this work were found for [Im(10.1)](+)[tcb](-); thus, [Im(10.1)](+)[tcb](-) showed the highest affinity for 1-butanol in a binary mixture. The experimental data were modeled with the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT). PC-SAFT was able to accurately describe the pure IL and (1-butanol) IL data. Moreover, the model was shown to be predictive and extrapolative with respect to concentration and temperature.