Epigenetic changes in gene expression due to DNA methylation regulate pulmonary vascular structure and function. Genetic or acquired alterations in DNA methylation/demethylation can promote the development of pulmonary arterial hypertension (PAH). Here, we performed epigenome-wide mapping of DNA methylation in whole blood from 10 healthy people and 19 age/sex-matched PAH patients from the PAH Biobank. Exome sequencing confirmed the absence of known mutations in PAH-associated gene variants identifying subjects with or without mutations of TET2, a putative PAH gene encoding the demethylating enzyme, TET2. DNA of patients with PAH and no TET2 mutation was hypermethylated compared to healthy controls. Patients with PAH and a TET2 mutation had greater DNA CpG methylation than mutation-free PAH patients. Unique Differentially Methylated Regions (DMR) were more common in patients with PAH with TET2 mutations (1164) than in PAH without mutations (262). We correlated methylome findings with a public PAH transcriptomic RNA dataset, prioritizing targets that are both hypermethylated in our cohort and downregulated at the RNA level. Relative to controls, functional analysis reveals enriched functions related to T cell differentiation in PAH patients with a TET2 mutation. We identified genes with downregulated expression that were hypermethylated in PAH patients (with or without a TET2 mutation). In both cases, a conserved T cell phenotype emerged. Pan-chromosomal hypermethylation in PAH is greatest in patients with TET2 mutations. Observed hypermethylation of genes involved in the pathogenesis of PAH, such as EIF2AK4, and transcription factors that regulate T cell development, such as TCF7, merit further study and may contribute to the inflammation in PAH.