The Mount Ida Catholic Cemetery, or Old Catholic Burying Ground, lacks its own sign to differentiate it from the Mount Ida Cemetery. It constitutes the land on the east side of Pawling Avenue that is south of where Balsam Avenue ends. Very few monuments are standing in it, most of them evidently laid flat in 1872 as indicated in the below Troy Daily Whig article.

Most of the interments date from the 1830s-1850s. There's apparently only a few from the 1870s-1890s, and (judging from visible headstones and the DAR's 1923 survey) none that date from the 1900s or later.

"the city, on January 1st, 1832, purchased twelve and three-tenths acres of land, to which was given the name of Mount Ida Cemetery, on the south side of the Poesten Kill, and east of the road to Albia. On February 5th, 1835, the city sold one hundred and thirteen perches [113/160 of one acre] of it to the trustees of St. Peter's Roman Catholic Church, which is now known as the Old Catholic Burying-Ground."
Weise, Arthur James. Troy's One Hundred Years 1789-1889. Troy, NY: William H. Young, 1891. 93.

St. Peter's Cemetery has a slightly newer cemetery in Troy, established in 1858.

"Most of the stones now (1976) in the Catholic section of the Pawling Avenue cemetery are flat on the ground and sod had to be removed before they could be read. There are only five still upright; three or four are inscription side down, and another two or three have crumbled to dust. Forty-seven stones in this section were uncovered, twenty-two of which did not state a place of origin and are not included here."
Nial, Loretta M. Tombstone Inscriptions In Cemeteries In Troy, Rensselaer County, NY Indicating a Foreign Place of Origin. 1976. .

"The Old Catholic Burial Ground has been, as is well known, a neglected place and in a disgraceful and ruinous condition for many years past. No attention has been paid to it by the public authorities, or those having friends buried there, and but few burials have been made there for several years.
"Last October, Dr. [J.T.] Luck and myself drew up a petition to the Common Council, asking permission to remove the old decayed fences, to lay down the tottering tombstones, to cut out the underbrush, trim up the trees, grade the grounds and put them in decent condition.
"That petition was signed by the people living in the neighborhood, by several having friends buried there, and by Father [Peter] Havermans and Father [Henry] Herfkens, both of whom recommended the project. [...]
"Before a single stroke of work was done, Dr. Luck and myself went to see Mr. [John F.] Kelly, the Superintendent of Burial Grounds, to get his direction in the manner.
"He told us to remove all the fences, to lay down all the stone except the monuments, to clear out the underbrush and trim up the trees, and put the same in a respectable condition.
"That work has been done at our own expense. Three of the men who did the work are Irishmen, and I understand, Catholics, and they unite in saying that no wrong or desecration has been committed, and that the place looks better than it ever did before. Every stone was carefully laid upon the grave to which it belonged; not a cross or stone designating any grave has been removed from it, not a mound has been obliterated."
Hayner, Irving. "The Mount Ida Cemetery." Troy Daily Whig. July 1, 1872: 3 col 3.

"A LAW RELATIVE TO THAT PART OF MOUNT IDA CEMETERY COMMONLY KNOWN AS THE OLD CATHOLIC BURIAL GROUND.
"Passed October 5, 1854.
"The Mayor, Recorder, Aldermen and Commonalty of the City of Troy, in Common Council convened, do ordain as follows:
"SECTION 1. If any person shall willfully, maliciously or wantonly break down, damage, deface or injure any part of the fence surrounding the burial ground on Mount Ida, known as the old Catholic burial ground, or shall break, remove or injure any lock or locks on the gate or gates of the same, he or they shall, for each and every such offense, forfeit and pay a penalty of ten dollars.
§ 2. No graves shall be dug or opened in said ground except by or under the direction of the superintendent of the public burial grounds of the City of Troy; and none others than those resident at the time of their decease in the City of Troy shall be interred in said grounds without the consent of the committee on public burial grounds, or the chairman of said committee, first obtained in writing. For each and every offense, he or they so offending shall forfeit and pay a penalty of ten dollars."
Municipal Ordinances of the City of Troy. Troy, NY: Troy Times Art Press, 1905. 215-216. .

Some people of Irish origin are buried in Old Mount Ida Cemetery. Henry Reynolds (1814-1855) and his young children share a headstone in the woods overlooking Lake Ida. Catherine Armstrong (1821-1881) has a large obelisk near trees alongside Pawling Avenue.

There were probably a great many more interments than are currently entered on findagrave. Some headstones might be buried; many people might never have had more than a wooden headboard or cross, long gone.