It depends on whether there is a letter next to the date.
Circulated bills with no letter, A, or B are worth $22 to $45 depending on the amount of wear they have.
However a 1928 C bill is worth $175-$500
Your bill is actually called a Federal Reserve Note, like modern $20 bills, rather than "a bank note of Chicago". Chicago is simply the Federal Reserve District location that distributed the bill. Please see the question "What is the value of a 1928 US 20 dollar Federal Reserve Note?" for more information.
A denomination is needed. Please look for questions in the form "What is the value of a 1928 A US [denomination] dollar Federal Reserve Note?" for specific information.
All 1928 $20 Federal Reserve Notes carried the phrase "Redeemable in Gold", although they weren't gold certificates. There were also gold certificates with that denomination but they have gold seals and lack the words Federal Reserve Note. Please see the question "What is the value of a 1928 US 20 dollar Federal Reserve Note?" for more information.
That phrase appeared on all Federal Reserve Notes of the time because the US still issued gold-backed currency, even though FRNs were not gold certificates. Please see the question "What is the value of a 1928 US 5 dollar Federal Reserve Note?" for more information.
1928-series $100 bills weren't issued as silver certificates, only gold certificates and Federal Reserve Notes. Please look at the bill's front to determine which you have; then check one of the following: "What is the value of a 1928 US 100 dollar Federal Reserve Note?" "What is the value of a 1928 US 100 dollar gold certificate?"
Your bill is actually called a Federal Reserve Note, like modern $20 bills, rather than "a bank note of Chicago". Chicago is simply the Federal Reserve District location that distributed the bill. Please see the question "What is the value of a 1928 US 20 dollar Federal Reserve Note?" for more information.
A denomination is needed. Please look for questions in the form "What is the value of a 1928 A US [denomination] dollar Federal Reserve Note?" for specific information.
It's actually called the Federal Reserve Bank of Chicago. However all 1928 Federal Reserve Notes had green seals, so please check your bill again and post a new, separate question.
"A" is the highest series letter for 1928 $50 Federal Reserve Notes. "K" is most likely the Federal Reserve District letter. The series letter, if any, on US bills is next to the date. Please see the question "What is the value of a 1928 US 50 dollar Federal Reserve Note?" for more information on values.
All 1928 $20 Federal Reserve Notes carried the phrase "Redeemable in Gold", although they weren't gold certificates. There were also gold certificates with that denomination but they have gold seals and lack the words Federal Reserve Note. Please see the question "What is the value of a 1928 US 20 dollar Federal Reserve Note?" for more information.
The green seal indicates that it's a Federal Reserve Note. Please see the question "What is the value of a 1928 US 5 dollar Federal Reserve Note?" for more information.
The green seal indicates that your bill is a Federal Reserve Note. Please see "What is the value of a 1928 D US 5 dollar Federal Reserve note?" for more information.
Regardless of the Federal Reserve District that distributed the bill, as of 09/2012 a 1928 $100 FRN retails for $125 to $180 depending on condition.
1928 $50 bills were issued as gold certificates and as Federal Reserve Notes but they're not the same. Please check the wording across your bill's top front as well as its seal color*; then see one of the following questions: "What is the value of a 1928 US 50 dollar Federal Reserve Note?""What is the value of a 1928 US 50 dollar gold certificate?"* Gold certificates have gold seals and FRNs have green seals.
That phrase appeared on all Federal Reserve Notes of the time because the US still issued gold-backed currency, even though FRNs were not gold certificates. Please see the question "What is the value of a 1928 US 5 dollar Federal Reserve Note?" for more information.
1928-series $100 bills weren't issued as silver certificates, only gold certificates and Federal Reserve Notes. Please look at the bill's front to determine which you have; then check one of the following: "What is the value of a 1928 US 100 dollar Federal Reserve Note?" "What is the value of a 1928 US 100 dollar gold certificate?"
Not every old bill is automatically a certificate so it's important to check carefully. If it has a gold seal and says "Gold Certificate", see the question "What is the value of a 1928 US 10 dollar gold certificate?" for values. If it has a green seal and says "Federal Reserve Note", it's not a certificate, it's a Federal Reserve Note. See the question "What is the value of a 1928 US 10 dollar Federal Reserve Note?" for values.