Solenopsis invicta Buren (Hymenoptera: Formicidae), also known as the red imported fire ant (RIFA), is currently established in many Southern and Central Californian regions. RIFA can be managed using various insecticides, but in recent decades, granular baits have become a standard and effective management tool. To improve and maintain effective RIFA management programs, researchers and pest control experts need to perform careful population monitoring before and after treatments. Despite the availability of various RIFA monitoring methods, many are challenging to perform and are extremely time-consuming. Counting mounds is an easier-to-perform method but may not be reliable in certain places and for detecting low-density populations. Other methods of field sampling and laboratory counting can be cumbersome, destructive, and highly time-consuming. In this article, we are providing research data on a new, fast, and nondestructive field technique for RIFA monitoring using density (ants/ml) measurements. These measurements can be converted into counts and eventually to indices. On average, the density of RIFAs inside our measuring cylinder was 130.8 ± 2.3 ants/ml (Mean ± S.E.). A strong positive and statistically significant correlation was found between the volume of RIFA workers and the number of ants (r = 0.92, P < 0.001).