In the fifth book, Sirius tells Harry that his father was responsible for the house being unplottable.
‘It’s ideal for Headquarters, of course,’ Sirius said. ‘My father put every security measure known to wizardkind on it when he lived here. It’s unplottable, so Muggles could never come and call – as if they’d ever have wanted to – and now Dumbledore’s added his protection, you’d be hard put to find a safer house anywhere.
Harry Potter and the Order of the Phoenix - chapter 6 - The Noble and Most Ancient House of Black
However in the following book, Dumbledore tells Harry that the Order were the ones who made the house unplottable.
‘Well, obviously we would prefer that she didn’t get it, either,’ said Dumbledore calmly. ‘The situation is fraught with complications. We do not know whether the enchantments we ourselves have placed upon it, for example, making it unplottable, will hold now that ownership has passed from Sirius’s hands. It might be that Bellatrix will arrive on the doorstep at any moment. Naturally we had to move out until such time as we have clarified the position.’
Harry Potter and the Half-Blood Prince - chapter 3 - Will and Wont