In Illinois, account numbers always have a prefix (a letter) preceding the function number. The purpose of this prefix is to distinguish between function codes that are used as both revenues and expenditures, with entirely separate meaning.
For example, the revenue function R1110 represents the Educational Purposes Levy. The expenditure function E1110 represents Regular Programs.
Example account numbers could be 10-R1110-1 and 10-E1110-110-1.
This chart shows all the function prefixes:
| Prefix | Function Type | Function Code Range |
| A | Asset | 100s-300s |
| L | Liability | 400s-600s |
| Q | Fund Balance | 700s |
| R | Revenue | 1000s-4000s |
| E | Expenditure | 1000s-6000s |
| S | Source of Funds | 7000s, 9000s |
| U | Use of Funds | 8000s |
For clarification on the S and U functions, see Sources of Funds and Uses of Funds.