Yes, was the answer to whether the United States prison buildup reduced the crime rate in its initial stage and whether the buildup reached the point of declining effectiveness. Results suggest that during the course of a dramatic increase in incarceration there was an accelerating diminishing marginal return. This study utilized data from the United States over 30 years with strong evidence that the negative relationship between prison and crime became less strongly negative as the scale of imprisonment increased. State-level data were provided on prison populations and crime rates covering the years 1972 through 2000, for all 50 states and the District of Columbia. The key independent variable was the State crime rate per 100,000 populations using the FBI’s Uniform Crime Reports (UCR) Index. Tables, references