A routing number is a 9 digit code for identifying a financial institution for the purpose of routing of checks (cheques), fund transfers, direct deposits, e-payments, online payments, and other payments to the correct bank branch.
Routing numbers are also known as banking routing numbers, routing transit numbers, RTNs, ABA numbers, and sometimes SWIFT codes (although these are quite different from routing numbers as SWIFT codes are solely used for international wire transfers while routing numbers are used for domestic transfers).
Routing numbers differ for checking and savings accounts, prepaid cards, IRAs, lines of credit, and wire transfers.
All banks usually have separate routing numbers for each of the states in the US.
You can look for the routing number on the check (cheque book) issued by your credit union or can search this website for free.