A portion of these dividends is U.S. Government interest. Should I checked this box if I earned dividends from Fidelity Tax-Exempt Money Market & Municipal Bond funds?

Muni funds are exempt from federal and your state. Your brokerage statement would have attached pages breaking down how much comes from where. This allows the proper state and federal deductions.

@gimhteoh 

...however that [particular box to check, on the page after the main 1099-DIV form, refers to US Govt bond interest that might be included in box 1a of the 1099-DIV.

You would have to check the specific mutual funds in the following list, to see if you can check that box....but, you must calculate the exact amount yourself.....or, if it looks like too much trouble to calculate (assuming any of your funds is in the list) you can skip that checkbox and ignore it.

https://www.fidelity.com/bin-public/060_www_fidelity_com/documents/taxes/2020-gse-letter-sai-funds.pdf