How many colleges in USA have football teams?

Prior to the 1970s, many states crowned mythical state champions through polls, but playoff systems have become nearly universal since then and most states have steadily increased the number of teams eligible to participate and total number of classifications. Though the playoff scheme and number of teams eligible varies, regional champions will compete in elimination playoff rounds - in a tradition borrowed from pro football rather than college - to determine a state champion for each size classification. The championship games are usually held at a neutral site, usually a college or NFL stadium needed to accommodate the larger crowds. Note that some states with large populations such as California and New Jersey only crown regional champions, and in some large cities, such as Pittsburgh and Los Angeles, public high schools compete in their own "city leagues" and may or may not ever play opponents outside of them.