St. Mary’s County, Maryland

(Profiled 2-4-21)

St Mary’s County, population 113,510 (2019), forms the tip of land where the Potomac River meets the Chesapeake Bay in southern Maryland. There are approximately 43,000 acres of prime soils scattered throughout the County, with the largest tracts of prime farmland in the southern part of the County. The County has remained primarily rural despite the fact that it lies only 40 miles southeast of Washington, DC. 

St. Mary’s County included a traditional transfer of development rights section in its zoning ordinance in 1992 in order to provide flexibility and preserve farmland and resource protection areas. These provisions preserved roughly 670 acres in the next ten years. In 2002, a TDR code amendment changed base zoning regulations, which increased activity, preserving more than 1,000 additional acres of land in the next four years, primarily on small, grandfathered lots that were severely constrained by environmental restrictions (St. Mary’s County 2017). 

Another amendment in 2007 reduced ways of circumventing the use of TDRs. For example, the county eliminated bonus density for design standards, LEED certification, or extra green space. As of 2007, developers could exceed receiving site base density using either actual TDRs or cash in-lieu. As of 2011, the cash-in-lieu option had generated $234,000. In 2016, the Maryland Department of Planning recommended that the transfer formula be simplified. However, the Comprehensive Zoning Ordinance on the County’s website in 2021 remains unchanged with regard to Chapter 26 TDRs (Maryland 2016; St. Mary’s County 2017).

Sending areas are parcels in Rural Preservation Districts (RPDs), a zone that allows only one dwelling unit per parcel, regardless of size, unless the site becomes a TDR receiving site as explained below. One TDR is allocated for every five acres of RPD-zoned gross land area. Sending site owners who choose to participate can choose to build on site or remove some or all of their development rights and transfer them to any person or legal entity.

TDRs can be used to increase residential density on parcels zoned RPD, RL, RH, RMX, VMX, TMX, CMX and RNC (in growth areas only.) The baseline density in these districts is one unit per acre with the exception of 10 units per acre in the RH and special requirements that apply in the RPD (explained below.) In all but the RPD, one TDR increases residential density by one dwelling unit. The increased density allowed through TDR ranges from 1 bonus unit per acre in the RNC district to 14 bonus units per acre in the CMX district. On receiving sites zoned RPD, the first dwelling unit built on a receiving site does not require a TDR but uses five acres of base density. Thereafter less acreage is needed for each bonus lot but each bonus lot requires more TDRs as depicted in the following table.

Density (units per acre)Number of TDRs
1 dwelling unit per 5 acres1 TDR per lot after the first lot or dwelling
1 dwelling unit per 4 acres2 TDRs per lot or dwelling
1 dwelling per 3 acres3 TDRs per lot or dwelling

TDRs can be also be used to increase non-residential intensity of land zoned RPD, RSC, RCL, RL, RMX, VMX, TMX, DMX, CMX CC, OBP and I at the ratio of 2,000 square feet of floor area in excess of a baseline FAR for each TDR. 

Categories of receiving areas are paired with categories of sending areas. For example, receiving areas can only be located in a Critical Area if they use TDRs from sending areas in the Critical Area. Similarly, TDRs cannot be transferred to a Resource Conservation Area from within an Intensely Developed Area (IDA) or Limited Development Area (LDA) or from an IDA to an LDA. 

St. Mary’s County allows developers to comply with TDR requirements using cash in lieu of TDRs. The amount is set at 120 percent of the average fair market value paid for TDRs in private market transactions in the previous year but the Board of County Commissioners can increase or decrease that amount. In 2011, the Board set the cash-in-lieu amount at $20,000. The County can use the cash-in-lieu payments to buy development rights or replenish the Critical Farms Program.  

By 2016, St. Mary’s County’s TDR program had preserved 4,107 acres, mostly with transfers between rural sending and receiving sites (Maryland 2016).


Maryland. 2016. Transfer of Development Rights Committee Report. Accessed 2-3-21 at TDR-committee-report-2016.pdf (

St. Mary’s County. 2017. Land Preservation, Parks, and Recreation Plan Update. Accessed 2-3-21 at Approved 2017 LPPRP.pdf (