Green’s Dictionary of Slang

1. the vagina.

c.1591		Shakespeare Comedy of Errors III ii: ant. s.: Where stood Belgia, the Netherlands? dro. s.: O, sir, I did not look so low.
1598		Marston Metamorphosis of Pigmalions Satyre I 35: Welcome from Netherland, from steaming stew.
1630		J. Taylor ‘Sculler’ in Works (1869) III 24: Lieutenant Puffe from Cleaueland is return’d, / Where entering of a breach was sorely burn’d: / And from reuenge hee’l neuer be perswaded, / Till the low Countries he hath quite inuaded, / When his hot wrath males Neatherlands to smoke.
1656		‘The Threading of the Needle’ in Sportive Wit in Bold (1979) 157: O that I durst but shoot a gulf I know, / Or in the Lower Countries my seed sow, / Or plough the bottom of that Netherland / Until my plough did fall, and I not stand.
1733		Gent.’s Mag. No. 3 May 263: I’ll quit that frail empire, which once I held dear, And let puny states your gross Netherlands share.
1788		Harris’s List of Covent-Garden Ladies 130: She [i.e. a French whore] has one quality which many English girls want, that is a certain cleanliness in the Netherlands [and] performs constant ablutions on the gulph of pleasure.
2007		Skins ser.1 ep.1 [TV script] Tonight [...] you finally pop the cherry. You finally get the VIP tour of Netherland.

2. the buttocks.

1823		Devizes & Wilts Gaz. 25 Dec. 4/1: ‘On, on, my brave fellows!’ roared somebody in the rear, giving me a prick in the netherlands with a bayonet.
1984		Partridge DSUE (8th edn) 786: late C.18–early 19.