The United Guitar Company of New Jersey is a difficult firm to find any information on. Most of what I have heard about them is from less that concrete sources. That they existed I know. That they took over the factory and plant of Oscar Schmidt in New Jersey seems reasonably reliable but how soon after the bankruptcy in 1939 I don't know and I don't think they did much pre WWII. After the War they made Guitars and Ukuleles certainly and possibly other instruments as well? I know they produced the Sopranos branded Penn for the Pennino Music Co I have read they produced Guitar bodies for John D'Angelico but personally I doubt this. I believe they made some of the Bobby Henshaw branded Ukuleles plus a number of other lower end brand American Ukuleles of the late 40's and 1950's, (like Fulton), but I have never seen anything actually branded the United Guitar Co. 

Exactly when they went out of business is a mystery too but they don't seen to be in business today. Most, if not all of the output I have seen it suggested they made, was 1950's or early 1960's at the latest so it seems reasonable to assume they were another casualty of the rise of the far eastern production? 

They are the main US contender as the maker of the ubiquitous Baritone that lots of US firms branded in the 1950's and 60's, (same headstock - same bridge and saddle - same double marker on the fifth and tenth fret - same rings around the sound hole - same extended fretboard with the squared off end), especially if you believe the "Made in U.S.A." stamp that appears in some of them? What I do know is, not Vega or any of the Chicago makers (Kay, Harmony, Regal ect), that get trotted out as the OEM, made them, but this still leaves Guyatone or Matsumoko from Japan, or Egmond from Holland as equally likely OEM's; or someone from Germany, Taiwan or somewhere else? I would be grateful for any firm information?