A fire which is believed to have been smouldering throughout yesterday was discovered at the District Orange hall on the Scarva Road in Tandragee late last night.
The alarm was raised shortly after 10.10pm with early reports indicating that a door had been forced open and a fire started inside.
An Orange Order spokes-man said extensive smoke damage appeared to have been caused to the building.
Earlier, Ballylisk Orange Hall, on the Tandragee Road, Portadown, had almost all of its windows broken and inflammable liquid poured inside.
The hall was then set alight in two places but neither fire took and firefighters, alerted around 3am, were able to contain the outbreak with only relatively minor damage caused.
Ulster Unionist deputy leader Danny Kennedy last night warned that Orange-men would have to start guarding halls unless action was taken.
He said: "This is a highly provocative campaign directed at exclusively Protestant communities and unless the Government and the authorities take action then Orangemen may feel the need to guard halls themselves."
A quarter of the Orange halls in that part of Armagh had been targeted during the latter half of 2007, the Orange Order spokesman said.
"This hall is only about a mile from Ballyworkan Orange Hall, which was attacked by arsonists before Christmas," he said.
"Security Minister Paul Goggins visited the hall in the aftermath of the attack.
"It seems clear to us that this nearby hall was deliberately targeted by people who have no fear of detection."
He said 27 halls had been targeted last year.