Experimental density data are reported for four 1-C(n)-3-methylimidazolium-based ionic liquids (n = 2, 4, 6), three with trifluoromethanesulfonate and one with a tetrafluoroborate anion, at atmospheric pressure and at temperatures in the range of (268 to 356) K. The buoyancy method was employed, using the microbalance of the Kruss K100MK2 tensiometer. At each nominal temperature 40 evaluated buoyancy and temperature readings in two runs were taken in most cases. Averages of density and temperature values obtained at the individual nominal temperatures are presented with an estimated total standard uncertainty less than 0.3 kg(.)m(-3) (2.5.10(-4) p) and 0.02 K, respectively. The 83 new experimental data points on the density-temperature relation of the four ionic liquids of interest are means calculated from about 3000 individual density readings, which have been altogether taken in the present study. Measurements on two samples of the same stated high purity from different suppliers were performed for two ionic liquids, to demonstrate the influence of the sample origin.