Convert Mixed Number 9 1/1000 to Decimal Form: Step-by-Step

To solve this problem, we need to convert the mixed number $9\frac{1}{1000}$ into its decimal form. Let's execute this in a series of well-defined steps:

• Step 1: Convert the fractional part to a decimal.
  The fraction $\frac{1}{1000}$ corresponds to the thousandths place. Thus, $\frac{1}{1000} = 0.001$.
• Step 2: Combine the whole number and the decimal.
  The whole number part of our mixed number is 9. To convert $9\frac{1}{1000}$ to a decimal, we simply add the decimal fraction to the whole number. Therefore, we have: $9 + 0.001 = 9.001$

Therefore, the decimal representation of $9\frac{1}{1000}$ is 9.001.

The correct choice from the given options is $\boxed{9.001}$.