It may be better to ask on one of these threads, if appropriate:
Those threads would have information more specific to whether you are receiving over-the-air (OTA) signals (an antenna), or a given cable provider and the title of the thread would attract the right eyeballs.
If you are getting over-the-air (OTA) signals (using an antenna), I can tell you that according to Federal law all analog (NTSC) TV transmissions over the air are required to cease by September 1, 2015, so that gives you the furthest out limit for analog over-the-air transmissions. All full-powered stations must have already converted to digital (ATSC) transmission by now, but there may still be some "translators" and possibly some low-power stations still transmitting in analog even at this late date. Also, if your TV was manufactured after March 1, 2007, it probably also has a digital tuner and you would have to kick off the TV's rescan to find the existing digital TV transmissions available in your area. Usually you can tell if the TV is tuned to a digital or analog signal by the format of the channel number: xx (e.g., 28) would be an analog channel, whereas xx-x or xx.x (e.g., 28-1 or 28.1) would be a digital channel (28-1 or 28.1 would be the primary channel of station 28, usually in HD; 28-2, 28-3, etc., would be subchannels carrying different programming and usually in SD).
If you are getting cable service, that is completely separate from over-the-air issues and is very dependent on your particular cable provider and location.
My very humble setup:
I would like to apologize to anyone I have not yet offended. Please be patient and I will get to you shortly. Crap I say