Slingerland was established in Chicago by H H, (Henry Heanon or possibly Heanon Henry?), Slingerland in 1912 with the help of his brothers, first as an importer of Ukuleles from Germany, but then they began to manufacture them, initially to sell to students of his Chicago Correspondence School of Music. 

In 1927 Slingerland, now an established Banjo maker as well, started manufacturing drums in response to Ludwig starting to make Banjos, and the name was changed to Slingerland Banjo and Drum Company. (this inter-company rivalry was fortunate for Slingerland but disastrous for Ludwig as it started just at the end of the 20's Banjo Craze. It enabled Slingerland to diversify and survive but the making of Banjos lost Ludwig so much money that they were brought out by Conn). During the 1930s there was yet another name change, this time to The Slingerland Musical Instrument Manufacturing Company. 

Slingerland's main brand of Ukulele and Banjolele was MayBell, sometimes hyphenated sometimes not?, (the company also made regular Banjos, Banjo Mandolins, Guitars, and Mandolins under that name). They also did a lot of OEM, sending similar models out unbranded so retailers and distributors could put their own branding on. Early ones would sometimes have a 5 point star on the headstock but not all of them, (and other makers used a similar star too), Earlier model banjos also had a rounded headstock top with a central point protruding from it, in later models the point was cut off to become a central concave indentation. I have seen it suggested, but from what I have seen not the case, that the fretted wooden instrument manufacture was at some point subcontracted out to Harmony, Regal or both. 

Other Slingerland brand names included College Pal and Songster. The company remained in the Slingerland family until 1970 though they didn't make fretted instruments after WW2. In the 1970s and 1980s, Slingerland changed ownership multiple times until it was acquired from Gretsch by Gibson in 1994. After Gibsons bankruptcy I have read the name has been sold on to Hoshino Gakki