The lateral extent, depth of densification, and environmental effects of dynamic compaction (DC) were investigated for a very loose to loose silty sand layer with thickness varying from 6 to 12 m in a coastal area in southern Iran. Cone penetration testing (CPT) was done at different distances from the center of the point of impact before and after DC. The increase in cone resistance at different distances is plotted versus dimensionless distance X/D (X = distance from center point of impact and D = diameter of tamper), and equations are proposed to describe them. The amount of soil densification decreased progressively until the distance from the center of the tamper increased to about 3.3 times the diameter of the tamper, beyond which there was no densification. The peak partial velocity (PPV) measured at different distances from the center point of impact was used to determine the environmental effect caused by the impact of the tamper. Equations describing the relationship between the weight of the tamper, tamper drop height, distance from the center point of impact, and PPV for this site are proposed.