Illegal dumping of municipal solid waste (MSW) is a common practice in the cities of developing countries due to poor MSW collection efficiency. MSW collection efficiency in most Indian cities is 50%–90% of per day generated MSW. The remaining 10%–50% MSW left uncollected every day constantly responsible for the accumulation of a large quantity of illegal MSW at every nook and corner of the city. However, there is no data available for mass and composition of uncollected and illegally dumped MSW; no field method exists to estimate the mass of illegally dumped MSW at city and intra-city scale. Current study develops a consistent field method for tracking the spatial frequency, mass, and composition of illegally dumped MSW and presents results for four neighborhoods of varying socioeconomic status(SES) in Delhi. Per capita, illegally dumped MSW found to be highest in the low-SES neighborhood(61 kg) followed by mid-SES(4 kg), and high-SES(2.6–3.5 kg). The per km2 quantity of illegally dumped MSW in a low SES neighborhood (5336/km2) was about 100 times higher than high & high-mid SES neighborhoods(51 tons/km2). Comparison between neighborhood annual generated MSW, and illegally dumped MSW indicates, only 67% of generated MSW in poor neighborhoods and 97–99% in other neighborhoods is transported to the landfills. Per unit area, scale up estimation of total illegally dumped MSW for Delhi was 606/km2 and 83% of Delhi generated MSW is transported to landfills of Delhi every year. In total, about 557 thousands tons of MSW accumulated and illegally dumped in Delhi’ s streets, roads and open areas.