Identify the Number from Base-10 Blocks: Counting Hundreds, Tens, and Ones Squares

To solve this problem, we need to accurately interpret the graphical representation of a number using squares. Such representations typically align with base-ten visual models which identify groups of hundreds, tens, and units.

Let's analyze the number of squares in each part:

• The top section has 8 full columns corresponding to 'hundreds'. Each column in this section represents 100, so this part signifies 800.
• The second section has 2 full columns denoting 'tens'. Each of these columns represents 10; thus, this section represents 20.
• The bottom section shows 1 column representing 'units'. This corresponds to the number 1 in the unit's place.

By combining these values, the number represented is given by:

Therefore, the number represented by the squares is $821$.

Referring to the given choices, the correct answer is choice #4: $821$.