Of the two most popular types of Banjo, the Tenor, or four string Banjo, tends to be more associated with Irish Music, indeed Irish Music enthusiasts have actually adapted the original Tenor Banjo, which has four strings, specifically to suit playing along with Fiddles & Mandolins, by changing the string guages & tuning the same as a Fiddle. The Tenor Banjo is played with a piece of plastic, called a plectrum.
The other most popular type of Banjo, is the G Banjo, & it has five strings, four long ones & one half as long which connects to the extra peg half way up the neck of the Banjo. Another distinction is that it is played with the fingers & it is this Banjo which groups like The Low Country Boys, & also Bluegrass & Appalachian groups use for their music.
To find out more about the various forms of Banjo, check out this page: 
The fact is, neither of these Banjos have really played much of a part in the Scots-Irish Music story here at home.
On the other hand, the 'Banjolin' & 'Banjo-Mandolin' would have been far more commonly played by country folks here, being generally much cheaper to buy, and both naturally tuned the same as a Fiddle.
However, there seems to be a lot of unnecessary confusion over these little instruments.
So I'd like to take this opportunity to clear up any confusion by trying to explain the difference. For a start, the Banjolin & Banjo-Mandolin are shaped like little Banjos, while the Ukulele is shaped like a little Guitar. So with the Ukulele out of the way, how do we tell the other two apart.
Well, in fact that's pretty easy because the Banjolin has - '4' strings - & the Banjo Mandolin has - '8' strings, & just in case you don't believe me, here is some evidence, including photos.
Photo of a Banjolin: 
Here’s a video clip of the 'Soldiers Joy' being played on a Gold Tone MB-800 Banjolin Video: 
& Soldiers Joy, 'Old Time' style, being played on a 5 String 'Gourd' Banjo: 
The Banjo Mandolin has 8 strings, more info here: 
The Ukulele is a different wee beastie altogether, have a look: 