It is believed the plaques, which contained the names of those who lost their lives in wars, were stolen between Wednesday and Friday last week.
A Nottinghamshire Police spokesperson said: "This is a despicable offence and we'd appeal to anyone with any information to call us on 101.
"We'd also appeal directly to the offenders and ask them to search their conscience and return the plaques.
"Local residents will have relatives who were killed in action and will be deeply saddened by this selfish and mindless act."
Beth Dawson, general manager at Clumber Park near Worksop, added: "The latest incident of theft at Clumber Park is particularly despicable given the nature of the target.
"These plaques commemorate the men who gave their lives for our country and they've been taken without a thought for what and who they represent.
"The plaques are estimated to be around 100-years-old and were funded by the 7th Duke of Newcastle.
"The theft has upset everyone at the Clumber Park very much and we urge anyone with information to come forward.
"We are simply devastated that Clumber Park has again become a target after incidents earlier in the year."
Anyone with any information about the theft of the plaques should call Nottinghamshire Police on 101, quoting incident number 671 of May 4.