National Health Investors, Inc., established in 1991 as a Maryland corporation, is a self-managed real estate investment trust ("REIT") specializing in sale-leaseback, joint-venture, mortgage and mezzanine financing of need-driven and discretionary senior housing and medical investments. Our portfolio consists of lease, mortgage and other note investments in independent living facilities, assisted living facilities, entrance-fee communities, senior living campuses, skilled nursing facilities, specialty hospitals and medical office buildings. Other investments have included marketable securities and, until 2016, a joint venture structured to comply with the provisions of the REIT Investment Diversification Empowerment Act of 2007 ("RIDEA") through which we invested in facility operations managed by an independent third-party. We have funded our real estate investments primarily through: (1) operating cash flow, (2) debt offerings, including bank lines of credit and term debt, both unsecured and secured, and (3) the sale of equity securities.
At December 31, 2018, we had investments in real estate, mortgage and other notes receivable involving 232 facilities located in 33 states. These investments involve 151 senior housing properties, 76 skilled nursing facilities, 3 hospitals, 2 medical office buildings and other notes receivable. These investments (excluding our corporate office of $2,471,000) consisted of properties with an original cost of $2,815,894,000, rented under triple-net leases to 30 lessees, and $246,111,000 aggregate carrying value of mortgage and other notes receivable due from 10 borrowers.
As of December 31, 2018, our portfolio included 143 senior housing properties ("SHO") leased to operators and mortgage loans secured by 8 SHOs. The SHOs in our portfolio are either need-driven or discretionary for end users and consist of independent living facilities, assisted living facilities, senior living campuses, and entrance-fee communities which are more fully described below.