The TESOL job market in the USA is organized differently from what most teachers are used to abroad. Unlike most countries where TESOL jobs can be found in private language schools of all sizes shapes and forms, TESOL opportunities in the US are mainly found in Community Colleges and Universities.
However, though not as big in number as, say, in South Korea, private English language schools do exist and can be found in cities and large towns in many US States, particularly in the Border States. These help cater to the massive number of language tourists who come over for short courses to learn English (the US is the number 1 destination for this followed by the United Kingdom, Canada and then Australia).
If you are a citizen of the United States or Canada, there are opportunities for paid jobs (or volunteer positions) also at religious organizations, non-profit programs that work with immigrants, and libraries. Check with local community organizations or colleges in your area, or consult with career advisers at your university.
To teach at a college or university you would need to be fairly well qualified - a Masters Degree is often listed among the job requirements - but there are also English language programs that offer opportunities to less experienced or qualified teachers such as the Summer Programs that attract international students every year and in turn create a demand for enthusiastic and committed young teachers.
However it is true that enrolment levels at English language schools in the USA are lower than before and have not really recovered from 9/11. The difficulty in gaining a study visa for English language study in the USA, combined with the ease of studying in the United Kingdom, Canada, Australia and New Zealand where more work opportunities are available, are seen by many as some of the reasons for the slowdown in the TESOL market in the USA.
Having said this, in the last couple of years numbers have steadied, and many schools have stepped up their relations with agents in order to recruit more students. The bottom line is... you have to look hard, but the jobs are there.
To teach English at a state school you will normally need to have a teaching license from the state in which you wish to teach. This is then supplemented by an ESL specialization. So you would become qualified and licensed to teach, say, History or Elementary School and then get an extra qualification to teach ESL.
TESL Opportunities in the USA - a look at what is happening in the US in terms of teaching right now.