To a bank, certain deposits are riskier than others. Electronic payments, like paychecks that get automatically deposited to your account, have to be available to you on the next business day after deposit. Checks drawn on and deposited into the same or another branch of a bank as long as it's in the same check-processing region as the deposit. In 1990, Regulation CC recognized that advanced check processing systems made holds based on geography increasingly unnecessary. There can be several regions in one state, and one region can comprise more than one state.
State lines are largely irrelevant in determining a check-processing region.
These funds must be available to you by the morning of the fifth business day after the day of deposit. The entire amount of a check is not always what's held. A bank is free to tier the availability of your deposited funds. Most of your deposits will not fall into the categories listed above in the next-day availability section because they are probably checks written to you by private individuals or companies. As with most government regulations, there are more exceptions than rules, so be sure to do your own research if you suspect your bank is not following the law.